Guess that's the way to go for now. Though your list isn't really what I'm looking for either, partly because some stuff is completely unrelated (what does "inflation", "disembodied penis" or "fidget cube" have to do with the image containing ponies?), but partly because a lot of stuff is from the show and I wouldn't mind seeing it — first of all, things like changelings or zebras are practically ponies, and second of all I am now realising that while there's nothing wrong with gryphons those would be excluded by a "pony" filter. (Also unless I'm reading your filter wrong, it would exclude all images containing at least one of those tags, meaning that e.g. Opal being present in an image would be enough for it to get excluded.)
Which brings me to my next question: is there any better way to search for content that is "show canon species only"? (Without EqG for my personal tastes, but that's easy enough to filter.) If "original species" was tagged comprehensively, that might in theory be a good tag to exclude, though anthro and human probably wouldn't be included. Still, assuming that's not well tagged either, is there again no choice but to simply build up a giant filter of species that can be white- and blacklisted over time?