Intriguing theory, but I'm not quite sure I agree. As far as I'm aware, Kanaya could see Prospit visions not because she's a Sylph, but because she's a Space player. See also: Jade Harley, who is quite notably not a Sylph but still had ample access to Prospit visions (which arguably ties Sylphs more to Witches). It's been a while so I don't recall if Calliope was directly confirmed to have outright visions so take that with a grain of salt.