As for not seeing his patrons talk about the compression artifact issues to him on his streams or w/e, it could simply be because they don't know it's there. They could think that it's part of the art or whatever.
I'm curious on what the patrons' reaction would be if someone would point out to his patrons how much artifacting actually is in Sciamano's art.
It's kind of hard to discuss with his patrons or talk to him about this if you need to pay to get the opportunity to talk to anyone in the first place.
Also, with no guarantee that anything will change even if you paid his patreon to be able to talk, you could just end up losing your money. Unless there's a refund service that patreon has that I'm unaware of.
As for the size difference .png would bring, I just tested it myself by saving one of his .jpg to a .png with medium compression because high compression saves negligible file space (couple kb at best), if any, at much longer save times.
2.9 MB .jpg becomes 6.1 MB .png, so pretty much 2x the file size, but I don't think that's a huge issue. File space is pretty cheap nowadays, with deals on 2 TB drives going as low as $30, that's like 2-3 trips of eating out with a full meal.
Not only that but if .png is to much to ask for, at least go for .jpg with better settings.
It's slightly going more towards cringe / karen levels over like $10
$10 could be different for many people. it could be cheap or expensive. I think it's fair for people to discuss if they're getting their money's worth or not.