I don't NOT support any of her points; again, I agree with basically all of them. I really just think "The Tragic and Totally Preventable Decline of FFXIV" is a bad title/thesis, because that's not what the video is about. The video is just "My (and Everyone Else's) Current Frustrations with FFXIV." I'm not sure there IS evidence she could've provided.
It's really hard to make a compelling argument in support of "FFXIV is in decline." I would not be surprised to learn that it is, but that's also purely vibes-based: as you said, we just don't have clear enough data over a long enough period of time to make that case definitively. And of course two weeks before one of the longest content droughts in the game's history ends is going to feel extra decline-y.