This is really valuable feedback, thank you so much for taking the time to write this up!
I definitely hear you on Depths and Forest - I think for Forest we could incorporate bumpers with a lot more HP in the later difficulties to balance out the item upgrades that you've gotten so it isn't just "spam anywhere and you'll win"
For Mirage, we've tried a couple mechanics to distinguish it further and nothing's felt quite right so far. We have plans to try one more spin on it, and we'll be adding a lot more maps as well to increase variety. In my mind I see Mirage as a survival horde game, and Flock as a chase sequence!
Thanks again so much for your thoughtful feedback, it's really appreciated and helpful!