Underrated post.
You can hide a lot of flaws behind fast rapping. Fast rapping is cool. There’s a time and place. But when you rap slower and more deliberate your strengths and weaknesses are each going to be more exposed.
And IMO it takes a lot of confidence to be a slow flow rapper like how Guru was.

Jay Electronica
Conway The Machine
I can think of others but it's more debatable.
Probably throw in Banks for sure