Sadly I've not yet had the opportunity to visit the Arts Festival. I'm curious why you think it close to EPCOT's mission? By default I don't think it does all that much.
I can see how an arts festival could fit - obviously in WS, although that would require arts and artists form around the world more than local US ones. With the problem that arts often do not adhere to borders. Except for boring nationalist movements, or crafts and the like that conservative regimes seem eager to promote as somehow expressing national virtues and traditions.
Arts could fit in FW - design drives progress too, moreso now than ever.
I do think the F&W festival is in itself actually a really good fit for WS. Global gastronomy has always been a main draw and focus of WS, as it should be. Gastronomy is the cultural expression of differences in climate, soil, and regional traditions. I dislike many aspects of F&W's actual implementation, but don't dislike it in itself.
Flower and Garden feels a bit more far-fetched, is not a great thematic fit that furthers EPCOT's story. My personal favourite festival though! The park never looks prettier! ♡
Holidays are just that, they celebrate the end of year festivities and don't really need to further EPCOT's mission, although I appreciate how they manage to give EPCOT's celebrations a distinct EPCOT angle.
For WS, the Arts fits in with the Imagination Pavilion. As a whole, just look at RoE... it has a whole section devoted to human culture especially as expressed in the arts, both fine and performing.