Whereas I look at it as a spell that is horribly broken and ridiculously overpowered.
Again, why should a 5th level spell be MUCH more powerful than a 7th level spell? Granting more HP, better attacks, more damage, potentially speed bonuses and movement types for longer duration than Tenser's Transformation. And, I'll repeat again, I would NOT have the polymorphed creature suddenly radically change behavior. But, when faced with a situation where an animal would likely react differently than a PC, I don't have a problem insisting on some sort of saving throw to act against the nature of the animal.
Used as a debilitating spell, it's not really any different than a Banishment spell, really. Which is lower level, so, basically, it's a higher duration Banishment with a couple of extra benefits. No problems there. That's fine.
But, as a buffing spell, it's WAYYY too powerful.
Heck, something as simple as limiting size changes would fix everything. You can only go same size or smaller. Poof, instantly fixed.