The problem with this take is that some of the advertisers in the esports scene like Intel and HyperX have been around for over a decade. I’d trust their marketing department /somewhat/ to also be taking engagement into account and not just viewer count.
It’s not until super recently that other brands have been going into esports advertising. Those newer brands, sure I can see them being lured by high viewer counts. But as an example, you can see the sponsors list in this page for the World Cyber Games 2005 https://en.m.wikipedia.org/wiki/World_Cyber_Games_2005
Samsung, Intel, Razer, etc.