Pixi’s speed is not from a lack of engine overhead. You can do bunnymark tests with other small web game libraries and they don’t get anywhere close to Pixi’s numbers. My brother even made his own little rendering framework and looked through some of Pixi’s code, but didn’t manage to get it much faster than Phaser.
Ages ago when I was first checking out Defold I did some bunnymark tests with a few different game engines and web frameworks. These were my results: (Bunny counts at 55 fps)
HTML5 (firefox)
Haxeflixel - 950
Defold - 1600
Phaser - 2200
Pixi - 17,000
Windows
Godot - 4600
Atomic - 5000
Defold - 6500
Britzl’s version that used go.animate() instead of update() was much faster: 4800 bunnies in HTML5 and 16,000 on PC, but of course it’s not an equal test then.