I have a hero worth 10 base AP, has added 18/3/9/3/9 for his stats. When I equip him with 2 items granting 0/0/4/7/9
(melee/missile/str/endu/armor) his AP cost jumps to 57.
Effectively, he becomes worth almost 6 other heroes.
Unit equips aren't quite as bad. But it still equates out to leveling being a -MUCH- more AP-efficient way to increase power. (which I agree with, leveling should be the most effective method, its the hardest) But in most cases, it seems I would rather go in with less equipped, higher leveled, and more numerous units. I haven't seen so much benefit in equipment (and i'm talking around the uncommon level) so as to equate out a 50% increase to a unit's effectiveness. (Which is the increase in AP it costs)
Add this to the cost of creating/repairing equipment, and I think my guys are going in naked from now on!