To follow the instructions, I'm choosing the way saving throw bonuses fall hopelessly behind save DCs for epic monsters.
I'm fine with a stupid fighter having to roll perhaps a 17 to succeed on an Intelligence save.
I am not fine with a character having to roll 21 to succeed (that is, impossible saves).
It just stinks of bad design. It's not elegant. And more importantly, it's not fun.
My solution is really only a suggested approach.
Make it so DCs top out at 19. The idea a 1st level spell gets DC 11 and a 9th level spell gets 19 is a good starting point.
Then, epic superhuge worldending threats like, say, Demogorgon or Tiamat, could perhaps have an ability that forces characters to
save at disadvantage.
You need to roll twice, but you can always make the roll. If you start thinking "but isn't that much like the idea behind bounded accuracy"... you'd be
completely right!
In essence, the designers forgot to apply their beloved bounded accuracy on saves. And that's hugely irritating.
Now, to the real reason I wrote - nitpicking your own suggestions!
My problem.*
Too much spellcasting. I think it devalues magic in general.
My solution.
First, I would go back and re-design the classes. I would make the so-called "half-casters" in 5e that are martial (Paladins, Rangers) go to non-casting status, and replace spells with abilities. I would allow the Bard the option of half-caster (college of lore), and weaken half-casting (I would also weaken arcane trickster and EK). In essence, "half-caster" would now be a subclass (College of Lore, AT, EK).
Then I would move Wizards, Clerics, and Druids to a Vancian system- you have to have particular spells memorized, then forgotten. Yeah, I know. I would limit the number of spells known to Wizards from what it is now.
Warlocks and Sorcerers (especially) would retain limited spells, but gain the (slight) advantage of flexibility in their spellcasting. More flexibility from a more limited palette.
Finally, I would greatly reduce the availability and potency of cantrips. I would get rid of attack cantrips completely; this is what weapons are for. However, I would increase the potency of spells; if you are using one of your (level) spells, then you should get more benefit.
Those are my thoughts.
While I understand that these views aren't popular with many people, my personal belief is that magic is more awesome when it is more scarce.
*I understand that this isn't shared by most people.
I symphatize with the desire for more non-magical subclasses.
1/2 casters and 1/3 casters are already weak as is, and it'd be wrong to change that. After all, the 3E Bard showed us that a jack of all trades should be at 80% of those trades. Not 50%.
What you could do, however, is restrict the increase in save DC for 1/3rd casters. In 5E their Hold Person and Fear spells can be just as devastating as a Wizard's, which I can somewhat see as a point of contention.
The Vancian ship has sailed, and I'm grateful for it.
I symphathize with the desire to get rid of cantrips. In my case it's not an issue in combat, but for worldbuilding.
Sure you don't need a dagger or crossbow, but that is not worth the way cantrips make the world seem like a videogame. A cantrip allows you to apply flame to an object continously. So you don't need firewood to keep warm - just heat up a chunk of stone or metal. You can melt things, letting you open locks. A cantrip like Mending absolutely wrecks local economies, since you never need another supply in your life.
So I don't need to remove cantrips entirely. But I do symphatize with the idea you can't cast cantrips nearly as free as you can chop wood or swing swords.
Problem: There's too much healing. It trivializes the significance of combat, since anything other than death can be recovered from almost immediately. It trivializes healing magic, since a Cure spell or healing potion is less powerful than a nap. It creates an unbelievable world, where the outcome of getting struck by a weapon isn't that you're physically wounded, and it's hard to take that world seriously.
Solution: Set the default healing rate to 5% of your maximum HP per day (minimum 1 per day). Get rid of Hit Dice, or require them to be used in conjunction with healing magic (like Healing Surges).
Stor right there Saelorn. What you're really saying is: you want less monsters and less combat in your world.
The only reason healing is as generous in 5E is because you want to get to the fun stuff - the kobolds in the next room.
If your PCs encounter fewer and weaker enemies (so that they can still win fights even without hit points) or spend more downtime recuperating back at the inn, that's quite okay.
But it's not the way most people play, and it's not the way published adventures are set up.
There's nothing wrong with your suggestion, except your idea it should be the default rule. As an optional variant, I don't have any problem with it. As a core rule, no - it's just not the D&D most people want.
I would nerf certain things. Here are some examples:
1) -5/+10 would become -5/+5 (or -5/+1d10) for both Sharpshooter and Great Weapons Master. There is currently too much upside to this.
2) I would deal with Crossbow Expert (and specifically it's interaction with Sharpshooter) by either
A) Make it clear that the hand crossbow can't be the same hand crossbow you're using as your primary weapon (you need a free hand to load!)
B) Outright outlaw the combination of the two
3) Nerf the moon druid. Absolute damage sponge with very little risk. Find a way to add risk to this.
4) Add an optional rule or rules of some sort to supress multiclassing abuse. Examples:
A) Limit multiclassing to 1st tier (You can't add levels to any class that you don't have at level 4)
B) Limit multiclassing to two classes
That's my list examples that I'd try to use to nerf overpowerful rules interactions (and the moon druid).
1) I'm afraid that's mathematically unsound. Making it a half feat (so -5/+10 is replaced by +1 Str or Dex) is by far the solution that combines "simple" with "working".
2) I suggest removing Crossbow Expert entirely
3) no opinion
4) A is on the right idea, except it's probably too harsh, and it doesn't stop first level dips. The idea is that restricting MC to first tier is not fun if you later in life decide you want to spread out, perhaps for RP reasons. It simply feels needlessly inflexible to not allow MC at every level-up.
B also has merit, only it does nothing to stop "abuse" other than triple-class builds.
How about
C1. If you are a multiclass character, the class with most levels is your primary class.
C2. Other classes are secondary classes.
C3. If you have one or more secondary classes with fewer levels than half your primary class levels (round down), you must take a level in one of those secondary classes when you next level.
So, if you dip Cleric 1, and then start taking Fighter levels, you will find that when you reach level 5, you must take a second cleric level. As a Fighter 3/Cleric 1 character you're fine (since 3 divided by two rounded down is 1, and Clr 1 is not less than this number). As a Fighter 4/Cleric 1 character you now have fewer cleric levels than half your primary class levels (since 4 divided by 2 is 2, and Clr 1 is now less than this number). Thus your sixth level needs to be Cleric, making you a Fighter 4/Cleric 2 character.
This gets rid of one level dips.
The rule is otherwise flexible enough to allow you to abandon one class, and focus on others.
For instance, I might be a Fighter 10 that suddenly wants to explore the Bard concept with a pinch of Rogue on the side. I could pick a level of Bard, but then I couldn't go back to Fighter unless I pick up five levels of Bard first: at level 16 I could take Fighter 11 since 5 is "not fewer than half" of 11 (rounded down).
What I could do, however, is go
L11: Bard (Fighter 10/Bard 1)
L12: Wizard (Fighter 10/Bard 1/Wizard 1)
L13: Bard (Fighter 10/Bard 2/Wizard 1)
and so on
The regular MC ability requirements would still be in place, so I wouldn't worry about restricting multiclassing to two classes. The requirements mean more than three classes is probably an impracticality.
So, I won't answer this exactly as asked, but I will contribute this:
I'm am involved in a weekend-long RPG convention that is likely to use all 5e this year (for the first time). We are trying to stick close to the PHB rules, because it sort of defeats the purpose of adopting a well-known system to then tweak the heck out of it. But there are two things we're likely to change:
1. Drop all of the "uncommon" races, leaving Dwarf/Elf/Halfling/Human. In this case I think it's probably more of a historical thing with the event and the past race selection there -- and for those coming to the 5e setting for the first time, Half-Orcs and Tieflings in particular are a lot to swallow.
Sure. Each campaign world has a right to restrict character races. I would hate for a player bringing along Volo's demanding to be allowed to play a Tabaxi or Hobgoblin. That's just player entitlement that needs to go.
In general, the only PHB change I would make is to drop darkvision for elves and half-elves.
It's just too easy to create a near-traditional party that is all-darkvision with 5E elves.
The traditional D&D party, Human, Elf, Dwarf, Halfling party is 25% darkvision, and that's okay.
But with 5E I have found players can and will choose Half-Elf instead of Human, and Gnome instead of Halfling. Voila you have a close to traditional party with 100% darkvision.
I simply dislike the way this makes humans (& halflings) the odd man out. Not having darkvision becomes a liability, rather than having darkvision is an asset. I hate the way "man, couldn't you pick half-elf instead? Describe your characters as having human-like ears. And we can skip the lanterns and gain huge stealth bonuses!" puts pressure on players to abandon non-darkvision as the default.
Switch back elves to Nightvision* and this problem goes away. WHen the dwarf is alone in having darkvision, he can't blame the human and halfling for not having it.
*) Low-Light Vision
Characters with low-light vision have eyes that are so sensitive to light that they can see twice as far as normal in dim light. Low-light vision is color vision. A spellcaster with low-light vision can read a scroll as long as even the tiniest candle flame is next to her as a source of light.
Characters with low-light vision can see outdoors on a moonlit night as well as they can during the day.