So after playing for a while, I have some thoughts. Right now it's too easy to cheese the system, especially early on, by just destroying one or two more enemies then intentionally losing. So your first game destroy one enemy and die. Then destroy 2, then 3, and so on. I suggest making stars awarded based on the number of enemies defeated in a game, or based on the strongest enemy you defeated, rather than the high score. Right now doing really well in your first game or two can easily cause enemies to be so powerful that it's almost impossible to progress. Another way this could be fixed is make stronger enemies worth more points.
Second, I think the enemies scale too hard at the beginning based on player stats. I'd suggest starting enemies with 0.5*player health and 0.25*strength, and gradually increase from there.
Lastly, I'd suggest making the boss based on how many enemies have been defeated, rather than just player strength. Maybe something like player strength plus enemies defeated. Similarly, make the boss score something like 2*defeated enemies.