On further analysis, I think I know what's happening.
Aim does allow for critical hits... so that's not a big deal.
I found a lot more about bows and arrows though.
It seems that when a critical hit is dealt, the 50% bonus from the weapon's attack power is factored into the equation.
In the case of Edge, it's probably more like the average of his katanas * 50% as the bonus.
In the case of Yang, it's just his natural attack power that's in use * 50% as the bonus.
For a bow and arrow, it seems that this 50% bonus is derived differently.
A regular bow+arrow attack power is defined as this:
Bow's Attack Power/2 + Arrow's Attack Power + Str/4
A critical hit based on this looks more like...
(Bow's Attack Power + Arrow's Attack Power + Str/4) * 3/2 is the attack...
I'm still fuzzy on the math, but it makes a ton of sense to me, since the Angel Arrows + Perseus Bow does more damage than a Perseus Arrow + Elven/Samurai Bow.

It's actually starting to look like this for critical hits..
Bow's Attack Power/2 + Arrow's Attack Power + Str/4 + Bow's Attack Power
The critical hit bonus for bows is effectively tripling the impact of the Bow.
Also, critical hits aren't shown for arrows for some reason in FF4A.