I agree that polymorph is lacking. There is so much you could do with polymorph you could have to turn it into another class. Like in dragon form. I think that people should get dragonscale hide, multiple attacks, a breath weapon, a crushing attack, a tail attack, flight. I'm sure they get some of that but not all.
The problem with polymorph is this. If it were done right sorcs, a class that is already very very very powerful, would gain another substantial increase in power. There are so many forms you can take. In the olden days we used to polymorph into old ones and sorcs could level by killing fystrysks under morea, which is not something I recommend now.
But if all the forms were more accuracte with their powers and abilities I think polymorph would be way way to powerful. For game balance reasons you get what you get, and what you get is still pretty good.

I won't argue though that it could be improved on.