I have to say that this game was super fun, it may be very difficult but it's the difficulty that makes this game very fun.
To me, this game is very fair. The player has enough movement speed to be able to dodge, attacks are quite dodge-able (even if the boss is at the center, you can evade all attacks), enemies can hurt each other. There are no attacks that seem impossible to dodge, and if the player gets hurt, then it's most likely the player's fault. So it depends a lot more on skill rather than luck.
This was very fun, I really enjoyed this. Only bug I found was that if the player is near the walls, they can't shoot parallel to it (like if I'm at the bottom wall, I can't shoot left to right since it acts like I'm hitting the wall even though I'm aiming slightly up, and if I'm at the left or right wall, I can't shoot up and down).