I can only give my tale:
Saw Kizuna Ai, thought that was neat tech, didn't pay much attention. Years later, saw some Miko clips in 2019 (not sure when). Her singing along to some music while playing Ark; her making music in Ark while singing
We Will Rock You in her own special way; and of course,
Nigga~. Didn't actually start to look more heavily into them until I watched some
Hamburgaga videos of Fubuki. Eventually the Aqua one pushed me over to investigate more. From there, around March/April, I looked into clips and streams from Fubuki, Aqua, Marine, Aki, Flare, and Korone. Doggo was the one that sucked me in, but wasn't enough to get me to oshi to the point where I'm watching every stream I could - that would be Coco, who got me interested in the whole connected scene (which was just Hololive in my eyes at the time).
So I'm incredibly biased, but Coco may indeed be the single most important
person when it comes to the
popularization of vtubers in the West - and for that, I
should hate her, but she still holds a place in my heart.
I think she was the great bridge. Vtubers may eventually have grown this large in the West, and they would've grown large in Japan, but without the US, I don't think we'd see the
level of increase so fast in Japan, and without Coco, the US wouldn't have given vtubers the attention it did.