It's wild if it's running at 400 fps because nobody has a screen that refreshes at 400Hz. Every frame rendered past the screen refresh rate is wasted compute. Easily solved by limiting the frame rate.
It's not running at 400 fps, the UI has the current global listener count next to a button that says "fps". The fps is only shown once you click that button. Weird design, I know.
What's wild about that? That's exactly what it's doing and what most uses of canvas/WebGL do.