A question... How does a Roman legionary throw a pilum, if he is standing shoulder to shoulder in a tight formation? You can try this yourself at home... try waving a broomstick above your head without knocking over furniture. The gladius is the close combat weapon for when formations tighten, and it's short for a sword.
In game I use loose formation for the same reason that IRL formations often allowed space prior to contact - to allow for effective deployment of weapons, and to allow for manoeuvre through ranks. Try withdrawing your archers through a shield wall - it works about as well as it would have IRL - 1/3 of the poor archers end up stuck running in a stationery position tangled up with the heavy infantry.
But I agree with you, some of the animation physics are crazy - I saw a horse fly 20 meters in the air the other day from an arrow.