I wish that when I gave them better armor or weapons, then the old default equipment that I can't take from them, would at least not encumber them to any degree. It is a pain giving them better gear because then they can carry less for you. When reallistacally speaking, they would toss the worthless junk or stow it in a chest back at the house, why not just give them some clothes to wear and let us equip them from the get go, or have them default to clothes once we give them better armor and weapons.
Yeah they shouldn't be encumbered by their default (non-removable) items. The problem with your proposition of having them clothes only could be a problem for people just starting out or swapping to a new hireling (without taking the old guys gear or a new type of hireling i.e. from a fighter type to a mage type) I think your idea of them dumping the old gear is more appropriate in this situation. It's quite disappointing that this doesn't happen (especially considering that they can just have the basic armor respawn on the character after dismissal and disappear after being rehired and reequipped.
You can give them clothes or something and when you take it out of their inventory they'll equip the best stuff, temporarily.
That's not really an issue at least not one I've ever had they will always equip the new armor I give them as long as it's better than what they already have (though its a pain sometimes if you want your follower to use only light armor [if its their primary skill] and have them just hold on to lets say an ebony or daedric chestplate they'll equip said chest-plate instead of the armor type they're most proficient with [in this case light armor])