Heya thanks for trying the game!
Can I ask what bugs you faced, other than the plane and battery bug? Thanks for reporting those, I have just put out a new version (v0.14) that fixes both! If you die in endless mode the game should end and force you to restart a new save - if that didn't happen then it's a bug.
Will think about the ESC key - I would have put it on Q but that's for toggling the bomb. The game is designed as a downloadable game in mind so the shortcut keys are built for those platforms.
Understood on the frostpunk comment - I'm more inspired by TDs than Frostpunk actually, so I am not too worried about it!
What do you not like about the perk fragments? The game is still evolving and still in the idea experimentation stage, so I am open to feedback and how to make it better!