The model that's doing AI Summary for search results - that presumably needs to be fast and cheap because of the scale - is still sufficiently bad as to give people a bad taste. Presumably they're frantically working to scale their better models for this use case. If you could get Gemini Pro on every search result the experience would be effectively perfect (in the sense of better error rates than what a non-specialist educated human reading the top results and summarizing them would achieve). That's years away from a scaling/cost/speed perspective.