I didn’t mean to use lossless for the web version, but for the offline downloads. If it’s lossless, it’s the same quality, but saves the user download time and disk space. Again, not at all important, especially not this early in development, but you yourself mentioned that there would be a lot more in the future, so might be something to consider at one point. (Edit: Also, optimizing PNGs took a lot longer that converting to lossless webp, and only reduced sizes a little, so I don’t think it’s really worth it)
In my personal opinion, reducing asset quality for the web version is completely reasonable, so don’t sweat it too much 😁 (Edit: I’m on Android so I see no difference in quality really, the screen is too small for that 🤷, and even on desktop, unless you try to find faults, reasonable quality loss should be fine)
JXL situation really sucks, could’ve been something great.
Lastly, webp has a setting called preset which you can set to drawing. According to the docs:
Specify a set of pre-defined parameters to suit a particular type of source material. Possible values are: default, photo, picture, drawing, icon, text.
Since -preset overwrites the other parameters' values (except the -q one), this option should preferably appear first in the order of the arguments.
Did you use that when converting to lossy webp? Could that improve the quality a bit?