I lived in Sacramento while Mayle played HS ball. He played against my boys more than a few times. He was a RB and LB in HS, but the kid was a physical specimen on basketball court as well. Even at just 6'2 he was dominant on the boards as a forward because he was a load when he boxed out and impossible to slow down when he was running down the lane, especially on fast breaks.
I am also a huge PAC 12 fan now and one of my best friends is a WSU alum so I've have watched Mayle as a WR quite a bit, especially the 2014 season. I am not saying that Mayle IS a better blocking WR than Dez, or anyone else on the team, currently. And yes, Mayle is woefully inconsistent, from his hands to his blocking to his consistency. But Mayle is a very physical and strong WR who has the ability to erase corners on running plays as well as break multiple tackles after the catch. Mayle is NOT quite the freak athlete like Dez, but he is a freak athlete in his own right. And when he is focused he is capable of taking over games. He is the only WR in PAC 12 history to post two 250 yard games in a single season.
He has his warts but if he didn't then he would not be a 4th round pick, or released from original team who drafted him after one season. But his potential is through the roof but his team has to be patient. I don't believe he has more than a couple of seasons playing WR, at any level.