BAB is quite a meaningless stat.
um .... Power Attack? attacks per round?
(there's dozens of things restricted to BAB; but those seem the most obvious and useful)
Because it's not possible to have a high BAB and 9th level spells? Because a 4th level spell doesn't grant full BAB?
Attacking at -10 and especially -15 is quite irrelevant, this is why BAB fails, as it becomes just a to hit bonus, and those are easy to get. For example, Mr. 55 Str War Troll at level 13 has a +32 to hit just from BAB, Draconic Polymorph, and Bite of the Werebear. Not counting all the other buffs that are possible. Or just Wraithstrike.
Fail. This is why you're an idiot, Sunic. It's been explained to you 10 different times in 5 different ways, nevermind the fact that you and the few people left who agree with you about AC not mattering keep propping up Wraithstrike for some reason.
Sure, he has 2 natural attacks that hit for d8+22, or maybe two attacks with an actual weapon that deal d6+33 and a bite that deals d6+11... A level 13 fighter with just regular Polymorph would have 3 attacks doing at least 3d6+20ish depending on his gear and a comparable attack bonus, plus the bite doing d6+5, and then all would benefit from Power Attack. If he power attacks for -5 then that's 3 attacks with a large Greatsword doing 3d6+30 and a bite dealing d6+10. Depending on the fight, his gear selection, and his feat selection, this damage could be MUCH GREATER (FBs would be especially scary), especially on a charge, and it's really not going to be worse at any point.
In other words, that fighter makes better use of your 4th-level Polymorph than your Wizard does of his 5th-level Draconic Polymorph and his 7th-level Bite of the Werebear, plus your Wizard would be able to stand back and cast a 7th-level spell that's actually, you know, GOOD.