If I was to Streamline 5e D&D…
I agree with a lot of the stuff here. It might make for a very cool 5e-based OSR. There's a few things I disagree with though, of course:
Ditch skills. Go with 13th age/Barbarians of Lemuria style Backgrounds/Careers as Skills. 4-5 per PC.
I don't know those games. However, one of the issues I've seen with Fate (which I do know) is that it's really easy to tie everything into your High Concept if you phrase it properly. "Since I'm a
Barbarian From A Magic-Hating Tribe, I clearly know enough about magic to be able to decipher these magical runes. I'll even spend a Fate point to do it!" It sounds like if you make backgrounds, careers, class, race, or something broad like that into a skill, you'd end up with a similar problem. (Unless, of course, those games do skills in a completely different way from how you're making it sound.)
Distinct types of spell lists like PF. Mage (Trad Blast and cast), Drudic (Nature stuff), Sorcery (Summoning things), Miracles (Cleric powers). The classes primarily learn and focus on the spells of their class, but make an in-game way to learn a few spells from others.
Personally, I like some of the wizard spells that don't fit into "blast and cast" since they're often very flavorful or mythic in concept, and that works well in a game like D&D. I'd be happy if they were more like unique rituals rather than just "ho-hum, I leveled up so I might as well take
tiny hut." But I wouldn't want to get rid of them.
Also, not to just list the wizard archetypes at you, but they mostly do fit standard tropes. You know of the enchanter, the illusionist, the necromancer, the summoner, the transmuter (or alchemst, if you like). They're all very D&D-style fantasy. Whether this simplified version has multiple mage classes and spell lists, or wizards who have to choose a type of magic when they're created--either way, but they should stay.
Which brings me to this:
Feats are gone. Subclasses are gone. Multiclass gone.
Subclasses. Actually one of my favorite things in 5e. While I know that you have class abilities you can choose from, the most important thing for subclasses is that they provide a theme, and random abilities won't cut it--especially since you can min-max to your heart's content this way.
Stop all HP progression at lvl 5. All other level increases occur normally. So the characters get more powerful, yet still retain a certain vulnerability to threats.
Personally, I'd do what they used to do, which is to give warrior-classes +3/level after they stop getting Hit Dice, squishy spellcasters +1/level afterwards, and +2/level for everyone in the middle. Or let people keep getting their Con bonus afterwards.