Physically, yes, Harrison is/was the superior specimen in body build and strength. Lambert was easily the better mentally prepared and stable player he played with a controlled rage each and every game and always knew what was happening in the game and manned his responsibilities. Lambert may have been "trucked" as you say, I didn't watch every game and it would be my bet that the trucking occurred simply because the back attained an advantage in angle, leverage or speed, not because they were mano-a-mano in the hole and he ran Lambert over like a rag doll.
I don't recall Harrison ever getting "trucked" to be sure but he is an outsside backer and is rarely taking on a running back that is running north and south like a middle linebacker in 43 defense would be doing many times per game. Both players could get off blocks and make tackles, Lambert by not allowing the blocker into his body (at 6'4" tall he had long arms) tio engage him and Harrison typically by brute strength.
Had Harrison had a longer career at a high level he would be a HOF candidate and Lambert was easily a HOF candidate and inductee.
Both players are great Steelers and will always remind me of great Steeler teams and defense. Selling one short because he played 30-35 years ago in a different era of football is silly.