Thank you for the detailed feedback! I did somewhat design the game to kill you with some patterns. There is one enemy mode that has some randomness which can become "kill mode" if you are unlucky with rng. The other 4 patterns are manually designed with a set pattern that can be 100% avoided with careful dodging.
Re: performance I played your game and saw you also used Godot. First is the longstanding issue of audio stuttering with HTML5 exports (which is being addressed with "Threads" mode in export) Another issue I've read about is Godot's performance with rendering many 2DNode sprites on screen. However I didn't encounter major performance issues in my game until I hit 3000+ bullets on screen at once. I did my own hit detection with simple distance formula checking. You might want to look into the 2D Bullet Shower Demo with godot and research Optimizing with servers for rendering sprites (I did not implement this in my game, but it is a topic I recently learned about that could definitely help with bullet hell games in the future!). What was your method of collision detection? Did your HTML5 version play at a low frame rate or did the audio just sound bad/glitchy? I find that when the audio is glitchy it tricks you into thinking the game itself is stuttering when it's actually running smoothly
But other than using the distance checking vs. 2D areas and built-in hit detection signals, I didn't do anything special for optimization