Yahoo had 90%+ of the search market and they lost it in a few years to google because they were unable to innovate. I don't think anyone saw that coming. Everyone was building "portals" (remember those? AOL.com? I think verizon.com was one at some point with news and weather) to try and compete with Yahoo's dominance in search. It can happen again. LLM Chat is certainly an existential threat to the googs. Part of the OpenAI lore is that google originally viewed it as a threat to their search/advertising revenue model and defunded it on that basis.
The fact that people are willing to pay for LLM and use it over search seems to indicate that Google's free product isn't as good, and llm chat is better "Enough" that people are willing to pay for it.
The major flaw in your argument is that Yahoo is still around. They still have tons of traffic, some of the most in the world, just behind Reddit. They are not constantly growing, yes, but that is exactly my point. They have a satisfied userbase who will use them for life as does Google. Neither is going anywhere any time soon. Both make billions of dollars annually.
Yahoo's peak (inflation adjusted value was ~$325 billion and the last sale of their assets was $4.5 billion in 2017 which is about 1% of it's peak value. I can't imagine google investors wanting to risk 99% of their investment.
The fact that people are willing to pay for LLM and use it over search seems to indicate that Google's free product isn't as good, and llm chat is better "Enough" that people are willing to pay for it.