You are all basing the premise of the argument incorrectly.
These are all assuming equal skill:
In a 1v1 inf vs inf battle, does the STR heavy or AGI heavy build win? The STR heavy.
In a 1v1 cav vs cav battle, does the STR heavy or AGI heavy build win? The AGI heavy.
In a 1v1 archer vs archer battle, does the STR heavy or AGI heavy build win? The AGI heavy.
I haven't played xbow or throwing since all the changes, so I can't really say much about them.
But the way the game is currently designed, each 'class' does better by leaning towards the proper attribute to build around. It just so happens that for infantry, it's strength.