Yeah so I later figured out the problem, turns out these downloaders only let you download the files that you're allowed to view, in other words anything behind a paywall cannot be bypassed and downloaded. But if u have access to the file it will generate a download link for you.i tried to install the extension and to use the script, but the "download button" doesn't appear
Kemono is really the only way to go, but the fantia importer has been broken for months. You may have some luck finding the creator you want on rule34videos or reuploaded on some other site, although this is much less unlikely to happen for smaller creators. But y'all already knew that most likely.
Since fantia seems to be mainly dominated by japanese, maybe there are other japanese sites out there that may have the creators you're looking for (still unlikely however). I'll keep y'all posted if I find anything