Oh! Sometimes I forget I have this one, but Burning Wheel could work!

Burning Wheel
Pros
  • Dice pool based system, meaning that results are relatively predictable.
  • Skills increase via use, but only if the roll would meaningfully advance the plot. Advancement is relatively slow, but encourages engagement.
  • The book contains some of the best advice for running I've seen, including saying 'yes, but..', failing forward, and the idea of 'let it ride' (you roll once, and let that roll stand).
  • Different stocks feel different, and most have unique magic systems (although dwarves don't use their, the humans and roden share one(/2), and trolls aren't smart enough).
  • Character creation is it's own minigame, which is relatively run, involving working out your characters rough backstory by going through a number of lifepaths..
  • The system designer rejected the idea of character balance in exchange for emulating what people would have realistically and narratively.
  • The entire system is in two really nice books.
  • Lifepaths are based on actual data for medieval france. Well, for humans at least.
  • Duel of Wits is the best social combat system I've ever seen (mainly because it focuses on convincing third parties).


Cons[*]It is quite complex.[*]The system designer rejected the idea of character balance.[*]Character creation takes a lot of time.[*]The system designer rejected the idea of character balance. No really, an elf or noble will just be better than a commoner.[*]It is very tied to medieval fantasy.[*]Duel of Wits, Range and Cover, and Fight! are relatively complex for theatre of the mind combat systems, involving planning your actions in sets of three before resolving the set.[*]Advancement requires a lot of tracking. Failed rolls, easy successful rolls, difficult successful rolls, as well as Fate, Persona, and Destiny points spent on rolls with that skill.

Easiness to GM
It varies, it's worth getting the book to just read the GMing advice.It's going to hard coming from 5e just because of the very different system assumptions.