There are more adult games than you might think, especially in the vn department, and there are new ones almost every time I visit (like twice a day or so), so using the individual game method would mean I'd have to exclude a new game every time I visit, and that's just tedious. Just go to https://itch.io/games/newest/nsfw to see for yourself.
The methods you've listed seem like more work than they're worth, just since I'd like for it not to be a thing I have to set up every time I visit. A couple clicks and boom, unwanted genres filtered out. This is why I feel the tag/genre exclusion tool should really be fully implemented, just to save from all the tedium and hassle. It just makes mroe sense that way, ya know?