Thank you so much for playing and for taking the time to write such detailed and constructive feedback! You completely nailed it with the delta time and FPS issue—I'll check the enemy spawn timers right away to make sure they are properly tied to Time.deltaTime so the difficulty curve works as intended.
Regarding the micromanagement and lack of action queuing, I completely agree. I am actually working right now on a new RTS-style squad system where aircraft group up at a Marshal Point before attacking. This should heavily reduce the elevator micromanagement and make the gameplay much more dynamic.
Thanks again for the support and for helping me build a better foundation for the full game!