> Their search could die and they’d still be the biggest advertising player

Nothing about their worth or whatever.

Google ad manager is the cornerstone of pretty much all internet advertising.

Even if you don’t buy ads from Google directly, somewhere in your ad pipeline is google ad manager.

That money is a part of Googles revenue, so there isn't as much there as you might think. Maybe you mean there is quantity there but advertisers doesn't pay as much for it as they would for Facebook or Google search ads, then yeah that is possible, but normally in a market segment you count big players by revenue and not numbers sold.