Mercs are only loosely related with plate mail, and it's not even about buffing Mercs. But everything is related with everything. I'm not making a game for you, personally. Your campaign is only one of many possibilities. That means 'multiple facets': my goal is to provide enough possibilities so each player can carve their own path. But to do that, everything has to have balance, some underlying order, because gamey balancing is lacking with so many objects. Mercs are hardly unbalancing if you're not using them/hating them due to personal reasons. However, if I don't give a skunk about training my gals, free maintenance unit with unlimited ammo, immune to any starting enemy, and easily killing any starting enemy - what's not to like? Gals can be always trained via Gyms, battle experience really isn't neccesary.