Nonsense. Valencia was/is always able to go forward with Mata on the wing and had a good understanding with him. I can´t believe such massive praise for a Man United fullback with zero offensive output. Obviously he´s solid defensively, but solid defensive fullbacks with good positioning are a dime a dozen. When Darmian is anywhere near Luke Shaw ability I will understand the praise. As of now, our attack on the right side is as dire as I´ve ever seen it.
Full backs that defend to an excellent level are certainly not a "dime a dozen." We're lucky in that we've got two.
Valencia is rotten going forward, we've seen more than enough to know that.
Darmian, meanwhile, has played a few games and it's likely he'll grow into the attacking side of the game. Full backs need to get it right at the back before they push forward with abandon.
It's patently obvious that Darmian is a good attacking outlet. He's demonstrated this elsewhere and it's clear he has all of the qualities needed to demonstrate that here at United.
That you're baffled by Darmian's popularity is baffling in itself. The right back position is filled with a quality player and people are duly delighted with that.