2 NecroFill
Yes, the map does seem a bit small. But if we assume that the fastest angels will move 6 squares, then 10 squares will be enough. Here's an example: chess has a small board, and the key is the mutual positioning of the pieces. I already expressed the idea on AG.RU that either the game will be incredibly tactical, where you need to consider a lot of nuances, or it will be total carnage. Time will tell!

And you're wrong about the single-player mode. In Heroes of Might and Magic III, there were actually 7 (or 8?) campaigns, not 6, but there were only 5 maps. So the single-player mode is standard.