I don't just mean after their 2nd and third record and than immediately plummeted, but where it was a long drawn out process of over 10 years at least.
Black Thought from the roots is the first one that comes to mind, it wasn't until the 00s where his flow started rly getting fluid and his voice became more distinct rather than sounding like every other 90s east coast rappers (he was great in Illadelph btw).
His best record is Game Theory but still got progressively better in Rising Down and How I got Over only thing is guests ruin the potential of his albums. Which is why game theory is the best roots record as it's the closest to a black thought solo.
Not to mention he's been killing guest features recently
And El-P I guess both as a producer and rapper though, my favorite record of his is Funcrusher Plus.