I agree. The equippable animals suits the comedic turn of the quests. I would prefer that it just stays as it is, all units can equip all items (except possibly weapon and shield being hero only as now, depending on what you think).
Btw: when you capture Trog Archers from the SK, you can't equip any items. It tries to, but when you close and open the equipment screen for the Trog Archer the item hasn't been equipped.
Also, some Trog Archers have the ability which is something like "Hero ability: can equip bow" but they can't. I'm not sure if that's intentional or not.