Really, balancing shmups is incredibly complicated, we had a terrible balance during the first days in our game, I learned a lot about this during the jam, especially playing Touhou in a specific way (not shooting), I recommend you do that aswell, it is very interesting to see how enemies actually work there, I was surprised that none of the enemies in Touhou stayed on screen, they always left to give space for new enemies, and when we put that in our game it made a whole world of difference.
I think this was also why your game was really hard to figure out, the enemies stacked really fast and had to focus just on surviving and it was very difficult to figure out a path xD.