linemen literally bash their heads together on every play. it would actually be a huge surprise to me if there was less head trauma at that position.
I mean, if I were an exceptionally speedy, brick-wall linebacker, I wouldn't get kicked out for causing extra concussions, I'd be given trophies and expensive contracts.
I think you are conflating speed and quickness. Offensive and defensive lines rely on quickness (i.e., acceleration) to beat the opposing team and make a play, while other collisions (e.g., tackling) often involve speed.
I am not saying that linesmen should not be expected to sometimes suffer head trauma; I was just noting that how often a player runs into another player is not the only factor.
Sounds to me like you're arguing for no reason.