I don't think there's much grounds for a serious legal attack at this point, and also it would look so horrible from a PR standpoint no non-desperate would dare it. Anyway, google has been steering enough traffic away, now that its AI jumps in with an answer and the wikipedia link which 99% of the response is based on is always hidden with a bunch of other overlaid icons. Google has surely managed to kill off a bunch of reddit and stackoverflow traffic with this trick.

on what basis?

Wikipedia is not a challenge to the system. If it were, it would be excluded from search results, much like blogs are now.