Firstly, apologies if I sounded snarky. My intent isn't argument, but discussion. We're all entitled to believe whatever we want to believe, and there's nothing wrong with that. That said, here are my issues with things as they are.
The whole thing is very deus ex machina, and it feels contrived (to me, personally). The two things that absolutely MUST happen for us to win, are two things our characters can never change.
Firstly, Tyrael must fall from the sky. Do our characters influence this at all? Nope, it just happens because it can. God within the machine and all that. Secondly, Azmodan has to tell us where to go, and what to kill. Again, do our characters actually have to figure out his clever plots? Nope, not at all.
When you combine these two elements, it makes for one very unbelievable third act. Not only do we require a deus ex machina, but we also require that the master tactician tell us exactly what to do to defeat him.
Here's the thing, though. If he's trying to demoralize us, why doesn't he just poke fun at us? That would humiliate us without risking his entire plan in any sort of manner. To me, that's the sort of thing an arrogant master tactician does. He pokes fun, he demoralizes, but he never does so at the expense of his own tactics. Azmodan, though, tells us exactly what we need to do to kill him, and not all at once, or in one 'oopsie I'm too arrogant for my own good' moment. No, he tells us in STEPS. "Oh ho ho, you've beaten my X, but you'll never beat my Y!"
If you're so arrogant that you don't back off after making one arrogant 'oopsie', then you're not very tactical. You're arrogant first, tactical second, and I just don't see that particular combination being a master tactician. To me, a master tactician is someone that puts tactics first. Each time, every time. He might make minor mistakes because of pride, but he will never divulge the entirety of his plot for essentially no reason.
Another point. Even if we don't have the means to defeat Azmodan, what kind of brilliant tactician is going to put more of his forces in harms way, purely for reasons of "YOU CAN'T BEAT ME. NYAH NYAH."? A brilliant tactician would not only be seeking victory, but victory at the lowest resource cost.
Furthermore, as to the demoralization, it actually works against him. It would only be demoralizing if the hero didn't succeed. The hero does succeed, and hence the entire thing would actually give them morale
. Azmodan, in his infinite wisdom, decides to try the exact same thing again, instead of changing up his plans. What brilliant tactician loses one battle, and starts the next battle in the exact same manner? If you played rock paper scissors with Azmodan, he'd simply yell out ROCK each and every time. He doesn't adapt, because he is a slave to his arrogance. That's fine and dandy, but don't then call him a master tactician. A master tactician can't be a slave to a flaw that would literally prevent him from ever becoming a master tactician in the first place. It makes no sense.
This is literally like if we invaded some dirt poor country and suddenly they had a legion of guys in Iron Man armor, even though it would be impossibe for those to exist.
Yes, but despite that the iron man armor doesn't exist, are we telling this third world country all of our military secrets? That's where the unbelievable comes into play. Again, even if he was certain
he would win, a master tactician wouldn't tell the enemy his every move. There are far better ways to insult the enemy (Satisfying his pride) and simultaneously protect his tactical advantage.
I think it comes down to a problem of characterization. When you build a character, you have to do so in a believable manner. Certain traits do not mix well together, and hence create an unbelievable character. Someone with so much arrogance -- Arrogance to the point where he literally stops thinking about tactics -- Is simply not going to be believable as a master tactician. If he were only arrogant to a point, and if his arrogance only gave us a slight advantage, it would make sense. But when he's so arrogant that he tells us every single thing we need to do to defeat him... Well, for me at least, that's gone beyond any semblance of believability. This isn't to say it wasn't believable for you. Perhaps it was. But for me, I found it entirely unbelievable.