Would be nice to get some feedback from the dev

Or, is the damage divided among the amount of ships you have? I can't shake the feeling something's off :-)

Or, perhaps, not all bullets are decreasing damage as they should at higher firerates. I just feel that the hitpoints decrease at a slower rate at some point. Or, in other words, ships with the same hitpoints don't get destroyed as fast as earlier in the game.

Yep, really love the concept and it's quite addictive, but the balancing sucks. Even if you don't make any mistakes at some point the ships become virtually understructible, it becomes more of an avoidance game than a shooter.

I also have the feeling that the damage resistance of the enemies increases. Not only the amount of hitpoints, but also the 'armor' so to speak, but that's just a feeling, I'm not sure.

It's a pretty fun concept and works quite well, however, I feel the balancing is quite off. Played a few times and always at some point I'm only able to destroy ships with really low health, while the ones with high health are virtually undestructible. I think the scaling (and division) of random health amounts can be improved a lot.