How is that gun critical any different from missing the same shot or having 4 shots in row connect?
Accuracy and penetration can be improved by microing your vehicle properly, and these things are in fact partly what separates good players from bad ones. There's no real counterplay to getting a main gun crit, so you're treated unfairly by the game regardless of how well you play.
Besides, why would having accuracy rolls in the game somehow justify having main gun crits? We can't remove accuracy from the game, but we could plausibly remove main gun crits.