Eh that’s stretching it. The only player who started a single game for that defense who wasn’t acquired AFTER the move and after BB was Rob Burnett. And Rob Burnett was actually drafted in 1990, the year before Belichick got there. He didn’t acquire a single player who started a game on that defense. Maybe there were offensive holdovers (I didn’t check), but they sucked on that side anyway. Giving BB any credit for those Ravens defenses is irrational.
But overall in CLE his first 4 years had a decent improvement arc before that unique fourth year. It’s not like he was some total flop of a coach the way some try to paint his record there.