and split the graphics into many small files so that the graphics are only loaded when needed and therefore quickly.
... many small files is precisly what the restriction on Itch does not allow for arbitrary reasons. It is a 1000 file limit. The size limit of the zip is 500MB, individual files 200MB.
https://itch.io/docs/creators/html5#zip-file-requirements
The size limit is explained on the faq. The file limit is not. Very large HTML5 games tend to be a poorer experience
There is this box hinting that they want to discourage engine exports. But as you just showcased, many small files is actually the way it would be developed directly in html5.
Or is number of files really a hallmark test to distinguish lazy engine exports to html5 from hand crafted html5 development? My guts tell me, it is the engines that would handle packed ressources better. On the other hand, I did see extracted rpg maker downloadables with like 10k files. But this brings me back to thinking, file number does not say much about the quality or the optimisation for web.
--
Oh, and I believe, if your game is only 50MB, downloading the whole chunk in one go is better for performance, instead of retrieving every tiny bit on demand. The exact opposite as html5 games were intended once. The concept is outdated or rather not optimised for all gaming scenarios. For complex online multiplayer games or such, loading on demand is better. For any single player experience with a "small" size like 50MB, one download should be better.