There's a reason why GSP (Generalized Second Price) auctions are called "truthful auctions", and that's because they elicit the true value as the bid from the advertiser (in theory).

So (in theory) advertisers will lower their bids if they're not getting the desired value from the clicks; and over time some will migrate budgets to other channels (like "influencers"? shudder ...).

Of course the big spenders on Google with the multi-million dollars advertising budgets won't just change their spending behaviour over night. That takes time - like anything in big corporations.

what channel actually provides most of these ad buys that would satisfy their ad dollars?

Google has been sued for being a monopoly, and it's not because they're just really good. It's because there's basically no other market that hits any of the dollar costs.

What other channels? The alternative on search is Bing and it's a tiny market. Then there's display which is total dog shit.