You should do a full write-up so we could have a proper look. Always hard to get a good overview when you need to mentally cut N paste yourself...For lower level magic and an S&S grittiness to the game a fast fix that works well is to do the following;
1. Reduce HP dice for PC classes to one-step lower (e.g. 1d8 becomes 1d6, 1d12 becomes 1d10 etc.)
2. Make all healing spells use up the healing HD of the target (or in emergencies the caster) on a 1 HD for each slot level of the spell basis (life force is burned to fuel magical healing...)
3. Make Paladins the Clerics (but they can access Cleric Spell List); Make Rangers the Druids (but they can access Druid Spell List) and the only 'full' caster the Warlock renamed as Sorceror or Mage with the following changes;
(a) Replace all but the 6th level Mystic Arcanum with an Eldritch Invocation
(b) Add Arcane Tradition of choice from the Wizard Class (now called 'Path of Mastery')
(c) Rename 'Otherworldly Patron' to 'Eldritch Bloodline' (the casters source of power)
(d) Rename 'Pact' to 'Arcanum' and the character gets Chain and Book variants
(e) Make Intelligence the spellcasting stat
(f) Use the Your Spellbook rules for the Wizard Class, this otherwise being the Book from the Warlock Pact
(g) Use Wizard Class Cantrip and Spells Known progression
(h) Use Wizard and Warlock Spell Lists
(i) Has Font of Magic like Sorcerer Class
(j) Remove Eldritch Blast from the game but allow all relevant Eldritch Invocations to apply to all damaging Cantrips
4. No Bards or Bear Totem Barbarians.
5. All magic items move up one step on the rarity table, so Legendary Items are considered artefacts.
6. Introduce 'Mastercrafted' items which either give +1 DR per class (lt/med/hvy) for armour, +1 AC for shields, +1 damage for weapons or +2 skill for tools.
A nice balanced 'low-mid' magic game will ensue
Unfortunately this only means nobody chooses to play a caster at all.
Even if there IS magic in the world, that world can still be called "low magic" as long as magic is evil and/or only for NPCs...No problem!
However it's all a matter of proportion. In fact, Conan, the granddaddy of all S&S characters faced powerful sorcerers capable on occasion of raising the dead, infecting entire armies with lethal diseases and enslaving the mind enough for people to kill themselves on command.
Not as 'low magic' as you might think, and this from the very progenitor of the S&S genre.
Agreed. Trying to mix the PHB classes in with a low-magic game is a painful combination. The core 5e chassis (levels, proficiencies, skills, Hit Dice) is pretty rugged, modifying the classes to fit the game you want is pretty easy. The question is how much work do you want to do to make new options presentable and digestible for your players.
All this does is shift the campaign's pacing from 6-8 encounter days (or fewer, if the party is successful in resting more often, you might have a 5-min work week instead of day, for instance). It can be a very useful thing to do, but it only makes the game 'lower magic' in a very desultory way in that magic systematically used during downtime will add up more slowly, it'll have no other meaningful impact on how the game plays out, nor the role of magic-using PCs in it.
It ('gritty' rest option) just creates a slower pace in the campaign, the non-casters also have to rest for a long time to get their HD back, for instance.
There might be one such sorcerer active in the world at a time, and no comparable power is typically accessible to Conan or whatever allies he may have at the time. That's low-magic compared to FR, by a huge margin, for instance.
I agree it's better to ban a class if the desire is to eliminate it from play, precisely because nerfing something to that is meant to be astoundingly rare in the setting, doesn't make it much less desirable for a PC, in fact, it can make it that much more appealing to a certain type of player.
A no-magic game or all-martial party is theoretically possible, it just needs to make up some basic capabilities that the game depends upon to remain playable and which existing non-magical classes lack. In 4e, thanks to there being more martial classes covering the three least dispensable of the four formal Roles, it was pretty nearly seamless - it would have been more so with a 'Martial Controller.' 5e has pulled back from that, a lot, with only a handful of non-magic-wielding sub-classes in the PH, but it could still be restored with enough work. There are a few more sub-classes in SCAG, and some in UA. There's any number of such classes of variable quality on DMsG. It's an obvious and profound lack, and there've been many attempts to address it, just no adequate, official ones.
