Not sure "enshittification" applies here, as Google isn't leveraging a middleman role to maximize revenue extraction from both sides of a transaction it facilitates, but I think you're right that Google does still have most of its eggs in one basket. Search and YouTube ads together still make up a majority of their revenue: https://stockanalysis.com/stocks/googl/metrics/revenue-by-se...
"Google leveraging a middleman role to maximize revenue extraction from both sides of a transaction it facilitates" is exactly how I would describe the google ads business.
Google Adsense is an intermediary between advertisers and websites. It operates an auction where advertisers compete to pay the highest for the space (squeezing advertisers) then it determines how large of a cut it can take before paying the websites (squeezing websites).
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.
A middleman is a specific party that mediates the relationship between two other parties. An aggregated system that everyone is using but no one in particular is in control of is not a middleman in the sense applicable here.
