In my opinion, armour and weapon upgrades break the balance of the game, just as well as valour bonuses from generals... This makes bow units less useful afer the mid-point of Early era. Having removed Armour and Weapon upgrades, archers remain a potent and a useful force. No more +3 armour Peasants or Fanatics with 20 man losses from huge masses of salvos ("then we'll fight in the shade!"). They never lose their usefulness as HA killers anyway, although Arbs usually work much better.

Arbalests, on the other hand, are never useless in my battles. They cause a lot of casualties, outrange almost everything, and force the enemy to make a move unless they want to get shot to death. A few units of arbalests work well even with cheap early units like spearmen and javelins supported with Mounted Sergeants, such stacks are perfect for ambushing and baiting even decent enemy armies.

One thing about the armour upgrades, though. They make Constantinople a much sweeter prize, don't they? +3 defence to Ghazi infantry is already a heart-warming idea...