Shapechange

[Cihparg]

So, the spell is 9'th circle, but it does not actually give any additional attack bonus, which, to be honest, makes it rather useless.
If you're a pure sorcerer, chances are, if you cast it, your attack bonus won't raise anywhere from your unarmed base.
That's an AB of anywhere between 10 and 20, even if you are otherwise changed to say, a Balor.
(Ofcourse, that depends on your level)

The form boosts your stats, that being abilities, skills, AC and HP - Which make them good for muling around stuff that you'd otherwise not be able to.
They however can't perform very well in Combat.

Therefore, allow Shapechange to profit from bonus AB, much like Tenser's Transformation does.
At the current moment, a caster with Tenser's Transformation is very likely to beat one using Shapechange.