Personally i disagree that the missile units are balanced but the realism shouldnt be hampered too much just to balance the game more(its not a blizzard or EA game afterall), also since its a totalwar game which have always been about massive realistic tactical battles.
While i dont want the game to be totally realistic because it would prob alter the gameplay too much, i dont think that altering it slighty will have such a game ruining effect. I know most people prob use the archers and crossbowmen to thin out the enemies numbers before a melee fight but as that is not the only purpose that archers and crossbowmen have i hardly think that this will be a problem.
As odd as this may sound to some, archers and crossbowmen are excellent ranged flankers. So the whole "lowering the crossbowmens rate of fire would be like lowering the number of units" wont be that much of problem if you use them as firstly to thin out the enemy numbers and then when the melee starts as ranged flankers, the crossbow still has a far superior punch then the longbow so they would still be able to dessimate enemy numbers cloes up.
I would like to see the longbow be a better morale devastator then it is now, because of the rather low rate of fire.

I really want the game to be more like MTW, and i dont think the crossbowmen in MTW sucked personally i loved the arbalests punch and range.

But some people, like me, would welcome the change and some people wont.