Honestly it makes sense as a move. Darkstalkers has repeatedly proven to be extremely niche, and while Capcom could fix that, they've repeatedly proven that they really don't want to take the risk of committing to anything other than a rerelease.
On the other hand, Darkstalkers characters have repeatedly proven to be super popular, and are the reason why the series has a noticeably high demand. So since Capcom sees potential in the characters, but no the series, Darkstalkers X Street Fighter makes all the sense. And hey, retconning the two series as one breaks Darkstalkers lore more than it breaks Street Fighters lore, so why not?
I don't love it, but I suppose the phrase "better than nothing" applies here. And NGL, I would be 10x more interested in Street Fighter 6 if I could play as a werewolf or a yeti or a giant mummy or something.