Maybe not less valuable but definitely less relevant. I think both are important.
https://en.wikipedia.org/wiki/Value_of_information
In the world of so-called "tech" companies, who use public information found on the www as "bait" to attract potential ad targets for data collection, surveillance and sometimes programmatic, targeted advertising, the information may have a value _to those companies, for that purpose_. They might measure that value by how popular the information is amongst www users
But I'm referring to the value of information published on Wikipedia to www users, not so-called "tech" companies who seek to intermediate access to free, public information that they did not themselves produce
But it can also mean "popular"
https://en.wiktionary.org/wiki/relevant
"Popular" information, evidenced by web traffic for example, may be important for so-called "tech" companies seeking to profit from intermediating access to free, public information, i.e., acting as a middleman. The information may be valuable to the so-called "tech" company middleman for purposes of supporting data collection, surveillance and online advertising services
However, the so-called "tech" company does not determine the value of the information to others. For example, a small group of people may find information on a web page to be valuable for their individual purposes. The web page may receive little traffic. The amount of traffic does not determine the value of the information to the small group
"AI search" might cause a decline in active users, but I cannot see how "AI search" would cause a decline in Wikipedia editors
Many Wikipedia editors are responsible for low traffic pages. I would imagine they are motivated to maintain these pages due to interest in the subject matter not interest in web traffic
Perhaps Wikimedia is only mentioning a drop in traffic as it suggests how www users may be gathering information, not because it is commercially significant, e.g., declline in audience for advertising
Indeed, it is okay for traffic to fall when a website is not trying sell out www users to advertisers. It does not mean the information offered by the website is any less valuable