This won't be the 1st time that something originally from an Amiga (7mhz?) cannot easily be done on a more modern machine.
This has nothing to do with the Amiga or 7mhz, or whatever... This is the difference between any paletted screen vs hi/truecolour screen.
On one case you just change the colour palette each frame... on the other you have to change every pixel's colour every frame: of course it takes quite a bit of CPU. Especially since it's running inside a browser with barely any hardware acceleration.
This is just called evolution: some tricks used back then because of the
limitation of the hardware just can't be used anymore... But are they needed ?
