They're obsessed with controlling followers inventories, you can't remove their base armor/weapons and it resets them after a period of time if you do (using the console). This leads to bugs like them not equipping the best bow they have or multiple armor pieces being added to their weight capacity.

I say get rid of this [censored] 'hidden base armor and weapons' crap, let us have complete control over what they wear etc, this would stop most the bugs with followers. Such an easy fix for these problems and allows you to have more control.

I hate how I gave my companion a deadric bow but she uses the wooden one :/

I agree for the most part but also in a way like that they will ALWAYS have a weapon just in case I for some reason removed everything.

being able to remove their armor and upgrade it would be nice.

Seems that followers actually do pick their weapon, but they choose speed(weight) over attack power. Try to put a longbow in their inventory. But yeah removing all that pointless hidden equipment would solve alot of the problems.

Followers default Outfit doesn't reset unless you take it all then dismiss the follower. If you take all but ONE piece then the Outfit will not reset. I did this with Derkeethus. Pickpocketed his Blades Outfit, except for Body, and his will not reset. (I made him a Blade before meeting Paarthurnax).

Only problem I normally have is with the hidden Bow. But that's fine with me. I gave Derkeethus special hidden fire arrows and that is good enough for me.