No one has said we won't be able to fight Alduin, at least no one in any position to know that has, myself, I think we will fight him. We must consider, In Oblivion, stopping Mehrunes Dagon wasn't really the player's destiny to begin with. Martin was the vhosen one, it was the player's role to allow Martin to get to where he needed to be to be able to stop the Oblivion Crisis, while just having Martin summon a deus ex machina to defeat Mehrunes Dagon made for a somewhat unsatisfying ending, but it did kind of fit in with how Martin was treated throughout the rest of the story. In Morrowind where it was your story, you did get to fight Dagoth Ur, it was a somewhat dissappointing fight, but you got to fight him, and I expect we'll get to fight Alduin in Skyrim, too, the only question is how it will be handled. I mean, we're dealing with a literal god who is capable of eating the world here, I think it will be pretty hard to pull that off in a way that does the concept of the fight justice, not impossible, but I think Bethesda will face a big challenge when it comes to making the final boss fight in Skyrim a satisfying one. And I expect Alduin will be similar to the other dragons, but bigger and stronger than all of them you fought before, so certainly, fighting him would put the gameplay of fighting dragons to the test and allow us to see just how well Skyrim handles fights against such large and powerful foes (Which past games didn't do a very good job on, but hopefully the fact that fighting dragons is important in Skyrim will force Bethesda to handle it better.)
In what way does epic boss fight at the end = shallow story?
Nothing, but don't bother trying to convince people of that here, the fact that you can have both is somehow extremely difficult for this forum to grasp.