All of those alternatives fail at debugging, because to this day browser teams don't consider 2D and 3D debugging tools something worthwhile having on developer tooling.
So in some cases you need a native build to try to replicate browser issues, and then being able to plug into RenderDoc, Instruments, PIX,....
Flash had the tools.
Safari's devtools has a visual <canvas> debugger. I remember using it, seeing all the CanvasRenderingContext2D calls that affected the canvas listed, and scrubbing left and right through time to see how a frame was built up.
Thanks for the heads up, at least that is something.