its generic search, when you go to vertical searches, say Amazon may beat google for shopping searches. Reddit can build good search one day, and many people including me will switch to searching inside reddit, instead of adding "reddit" to google search query.

You are right, google is currently generic search monopoly, but we were talking about ads, and there are plenty of other ads verticals.

Google has a number of advertising businesses, largely distinct. I think Youtube, adwords and adsense are the names of the three big ones. Adwords is a monopoly (that is, only Google sells advertising on www.google.com) and Youtube is too. But you didn't mean to to say that Google has a monopoly on selling ads on google.com and youtube.com, did you?

I think you had the third business in mind. That's the one that serves ads on third-party web sites. And what does Google's 92% market share for search have to do with its market share for that business? Or, put differently, how does Google's 92% market share help sell that product to more web site owners?

I though cloudfare has some way to onboard other bots too.