While I have very little interest in defending this garbage, I'll comment to a couple of points anyway.
I'm pretty sure the reason the worms weren't used by the orcs is >because the movie makers realized that having them be the >centerpiece of the battle would necessarily completely alter the >nature of the battle and stray too much from the source material. >Each one of them is just as big of a problem for their enemies if >not more so than Smaug would have been. It's not because of >some reason that makes sense in-universe. I have expectations >of things we will see more of in the extended edition (I'm hoping >for a dwarvish mountain ram cavalry), but I don't really expect the >worms will be one of them. Because the worms were not in the book, it is easy explain them. It may be, for example, that the orcs didn't really "have" them but were aided by them. While it was completely stupid to include them in the first place - especially without an explanation - my thinking for the whole time was that the worms were semi-wild (when they are mentioned in the book, they are called "wild") creatures that lived elsewhere. They aided the orcs to get to their destination for whatever reason (which was kind of on the edge of their habitat) but went back directly after that. To me this makes in-universe sense.
I know that's what you're sort of supposed to think, but it doesn't >make sense. Dain their commender was still alive. None of the >dwarves were fleeing. They weren't scattered, but instead held >together even as they were being pushed back. Lack of morale >wasn't their problem. They were outnumbered and overpowered. >The only reason they were pushed back in the first place is that >even when attacking at their original full capacity (and full morale) >the dwarves couldn't defeat the superior orc army. I don't know if something like "full morale" can even exist and I don't think the dwarves would be in full possible morale in the beginning of the attack no matter what. In technical terms I'd put it like this: In the beginning of the battle both armies expected to prevail. When the battle went on, it began to seem like the orcs would win, which increased the morale for the orcs and decreased it for the dwarves. When Thorin's company joined the battle, giving the dwarves some new hope, their morale went back up (I'd guess your king joining the battle in the front line would boost morale even beyond the starting point but I suppose that's debatable and doesn't really matter). This unexpected charge by the dwarves then lowered the orcish morale for some time, turning the tide of the battle for a bit. In the end the eagles (I think in the movie this was not shown very well but they are actually the fifth army, so it's not just a bunch of eagles joining) arrive and change things more thoroughly.
But I do agree that a lot of the battle didn't make much sense. Then again, a lot of the trilogy made no sense in so many levels that for me the battle is the easiest thing to forgive (it's not like cinematic battles are known for their realism even in non-fantasy settings).