froch and hatton come to mind straight away for me. especially hatton. plain to anyone seeing his early career vs his championship days he wasn't as good. with froch, hard to say but his power isn't as prevalent however his skills have improved massively. martinez at mw. hard to say how good he was when he was younger due to his inexperience.
One could argue that Danny Lopez was never quite the same after the ass whoopin' Bobby Chacon put on him.