Thank you for the detailed thoughts!
In terms of number of different characters, as this game was created for a two month gamejam, we had to limit the number of characters to have a manageable amount of art to create. We also decided to balance summon costs toward being able to more easily obtain all the units without too much grinding, because we wanted to see what combinations of units players would use.
(Not to say at all that your criticism isn't misplaced! But hopefully our decisions make more sense in context.)
We're not sure if we'll be revisiting this game, again since it was created for a gamejam, but we'll keep your comments in mind if we do make additional changes.