Old Zeratul was one of the strongest heroes in the game given his skill ceiling if you picked very specific talents. The change smoothed some of that out and requires you to make some sacrifices vice being able to do everything.
I think Zeratul is in a great place right now and has three extremely viable builds, all of which scale well with skill. But old rewind Zeratul was on a different plane of “busted” and deserved the changes he got.