Incorrect. Quality is a moving target as search gets better. Competition is in quality and distribution. If Google stops improving and lets Bing move ahead on quality, it'll be dead. Witness the recent worries about incorporating LLM's into search.
> Furthermore no one, including Microsoft, is going to risk $20B on overcoming Google's brand preference.
Earlier this year there were reports that Samsung was considering switching to Bing, and it was suggested there was a similar $3B contract involved. So of course Microsoft is in the same game, and it's quite obvious that Google wouldn't be paying these sums at all if Microsoft weren't willing to offer something as well (but keeps getting outbid).
E.g. if Google weren't paying Apple $20B, it's quite likely that Microsoft would be paying Apple $15B instead. One of them would be.