I was informed that companions are static to a level range based on when they first met you, like if you meet Lydia at lvl 10 she'll only scale to about 25-30 as to where if you meet her at 20 she'll level to about 35-40. '
I dont know how accurate this is but if it is true then I would like to request a mod that allows companions scale to the player. If it could be taken further to allow assigning perks, that would be great but i heard that perks dont work on npc's.