As expected, it seems like KOS-MOS' time hasn't come yet but with 6 confirmed new fighters, she definitely still has a shot!
As for Byleth, I'm actually pretty happy with the reveal as I've been a huge Fire Emblem fan since FE7 first released in the west and Three Houses has been one of my favorite games of 2019. Even though there are a LOT of FE characters now, at least I'm happy we got a character that I have a personal attachment to, unlike with Arle or someone else. Considering that Three Houses is the best selling FE and also one of, if not the best, FE ever made, I can see why Nintendo and Sakurai wanted to put him/her in the game. It kinda sucks that now Three Houses is getting all this heat simply because of Byleth's inclusion in Smash since it's such a great game but I guess it's to be expected with how toxic this community can get unfortunately. I'm pretty satisfied with this fighters pass though since, as a big JRPG fan, I got both Persona 5 and Three Houses reps, with DQXI's Hero being a cool inclusion too despite me hating his RNG mechanics.
I think my biggest concern now is that KOS-MOS may have to compete with Rex/Pyra/Mythra for a spot in the next fighters pass as I don't see both of them making it in. With Sakurai directly mentioning that he wanted to add Rex/Pyra/Mythra to the original roster, I'm expecting that they have a very high chance of making it, severely reducing KOS-MOS' chances. While I would be super excited for them as a huge Xeno fan in general, KOS-MOS is still the one I want most as a Xeno rep so I'm still a bit disappointed she didn't make the cut this time around. I'm still rooting for her though and won't give up until Nintendo confirms that no more DLC fighters will be added!