"Moving on from microlinebackers?"
This sounds like a personal wish of yours, seeing as the Bills just signed Bernard to a 4 year extension... 5 weeks ago.
Jack Lambert wasn't heavy but he was a pretty rangy guy... 6'4". Possible you're thinking of his teammate, Jack Ham?
While most player back then were smaller, linebackers were often bigger than they are today because at the time, there was more emphasis on stuffing the run. Nowadays it's just as important that LBs aren't liabilities in the passing game.