I do agree, Google and probably Meta even more so are likely to be impacted now just because they've become so overwhelmingly dominant. There's nowhere else left to cut for a lot of brands.
What will be more interesting though is if that money comes back to Meta or Google, or if people will find new, better opportunities while they pull back (eg. what happened to TV in 08).
Meta are concerned about this and already trying to book in bulk sales for next year with agencies which is something they've never done before https://digiday.com/media-buying/meta-moves-into-controversi...
Interesting. Preselling ads huh?
I think your point about dominance is a main player. I can make a dozen cases for LLMs as world of opportunity and compliments for both of these companies.
It takes a lot of opportunity/gain to hedge against the risk of losing 20% of search or social media revenue.
If you already have the whole market, losing share is easier than gaining.
But to a dominant incumbent..."threat" just tends to come with bigger multiplier.