Hey I have found that if you gave your follower a bow and stronger arrows, he/she will not use the bow, just the arrows. BUT the fix is in this:
If you want your follower to use a bow you give to him, you only have to give him the bow and NOT arrows. For example if you give Aela a daedric bow, just give her the bow and not the daedric arrows, instead if you want her to carry more arrows, give her some of her DEFAULT arrows (the iron arrows I think).

Hope this help any of you with trouble with your followers AND I hope bethesda really fix this problem later.