The controls I struggled with, it went through even worse iterations. The issue was players naturally want to click to place a new creature but also sometimes click to view handbook page of the unit clicked on, and it wasn't easy for me to come up with a simple way to distinguish the two apart from what I landed on. Re: tutorial, I agree, that's something I wish I had done better than text strings.
Regarding theme, one layer is the less spawns is more skill, but also the concept of creature transformation; the number of creatures is always conserved but they transform, meaning less of one creature always means more of another (different way to think of Less Is More). At least that's how I rationalized it :) . Thanks for feedback!