Eh, I'd say it's a combination of different things. The "FFXIV > WoW" hype this year was in swing before Asmongold made the shift. Near the end of last year, you had the ARR revamp. Soon after that, you had a ramp up in advertising for FFXIV, which soon led to a lot of
memeing about how aggressive FFXIV evangelicals can be (people started getting really annoyed by FFXIV fanboys constantly pestering them to play their game).
I think the thing that really started setting everything into motion was how much of a nothinburger Shadowlands turned out to be. With every prior expansion, a WoW expansion was a big deal in the gaming public's eye. Even though Legion and BFA's launches weren't anywhere near as big as WoD's, there was still a lot of buzz about BFA on the front page of PCgamer and such. But then with Shadowlands, not a blip. Hardly anyone talked about Shadowlands outside of WoW forums. Shadowlands' launch seemed to have gone relatively unnoticed. Furthermore, for people who were still playing WoW, Shadowlands turned out to be quite the disappointment. None of the changes Ion had promised came to pass. The game was still crappy as ever. Then, starting around Spring 2021, several months had passed since Shadowlands launched and there was no patch in sight, so people started grumbling. That was when the new FFXIV player records made their rounds. Meanwhile, WoW's biggest competitor started hyping up the next expansion, and got a new patch. Burning Crusade classic was released at the same time as a FFXIV patch, but quickly fizzled out. Then Belular started talking about FFXIV, and that's what really started the cascade in the media's eye. Then WoW 9.1 came out and was received rather poorly (which followed a string of PR blunders for Blizzard, with Ion's interview with Preach, Ion blaming his customers for his product not being fun, etc). By this point, the "FFXIV > WoW" narrative was already in full swing. Asmongold trying out FFXIV was just the icing on the cake.