Well, personally, I thought that chapter III would have Corvus in certain provinces acting as "Dragon" when entering a RTS battle. I thought that when Maxos spoke about demon's shards spreading the land...

I agree that bringing a Dragon vs Dragon AI to one last battle could kill gameplay flow, but introduce the mechanic during all the RTS battles on chapter III could have solved that problem. Although I like the idea, the compromise to achieve a good balance between micromanaging and diversion would be difficult.

I like the "only dragon" idea, too. Maybe with some little tweaks when ordering units in dragon form could make it possible. But yes, lots of problems raise... as the idea of "last boss" I think it sounds better in paper; make them actually work would be a different story.