The AI summary might help in terms of a phrase search, but it doesn't help at all really in terms of search keywords.
They're already dropped keyword search. The results are videos that have something related to videos that have something related to the words in the search; not videos whose closed captions or description contain the keywords.
If you go to Youtube without logging in, clear all cookies, and do a search on
Neal Asher, you get exactly six results with Neal Asher in the title, followed by tons of some kind of AI-curated results with nothing to do with Neal Asher directly, only indirectly (say, via Sci-Fi, or anything similar to the term "polity"), interspersed with a few videos directly mentioning Neal Asher.
Youtube search is utterly fucked already, and these changes definitely won't make it any better, only worse. The AI summary just makes it easier to obfuscate the search algorithm, by giving a plausible excuse, but actually allowing Youtube to curate the results based on what monetary value they can get from the user viewing those videos. They're not interested in serving the users what they want, but to maximize the profit from what users do view.
Which I understand perfectly from a short-term business perspective. It makes Youtube less and less useful for myself personally, though, pushing me to switch to the competitors (even though they have fewer content creators).