But amount of users is actually more a product of marketing than any technical protocol so I don't really see that point either. Also I don't see that being true, especially if you count in all the threads users.
My point of it being a W3C standard is more that it is a protocol that is in somewhat responsible hands. When using a protocol that was developed by and only for one (commercial) application in minds other players are always one step behind.
Mastodon (or threads) as the main platforms that implement AP don't have any more influence on the protocol than any other platform as well.