Not true except for GvG guilds. I have an awesome GE focused guild on Y that has multiple mobile players, and they are at least the equal of the PC players.
Again, not true except for GvG guilds.
Some of the mobile players I've seen are more active than I am. And I lead 3 guilds.
How? Other than GvG.
Heck, half the PC players don't know it's there.
That is just factually wrong. The only advantage on PC is that if you aid from Event History you can tell who's aiding you. Aiding from the guild/friend/neighbor list is faster and easier on mobile.
Where do you get these "facts"? You apparently are out of touch with how modern technology is used. You should hang around with more people who are comfortable with mobile technology, it might open your eyes.
Bottom line is good guild leaders judge players on their own merits and not on what platform they use to play the game. The only exception to that would be guilds that are heavily into GvG. And even they would probably take a few active mobile players who could help fund the guild Treasury especially if they're in an era where the guild is short of members. After all, the sieges and DA slots have to be paid for by somebody.