I suppose you're right, and it does apply to Google acting as a middleman between advertisers and content providers.

I do think the dynamic there is still a bit different from where the term usually applies, since advertising involves three parties in addition to the middleman, not just two -- the above comment was looking at things from the perspective of end users, in terms of where they prefer to watch videos, and that actually may represent a constraint on how much "enshittification" can happen that's particular to this industry.