They are so different that it's not really worth comparing them.
JuJu had 11 catches of 25+ yards last year, which is about average for his reception total. He also did pretty well there in 2015 with 16. That was tied with what Corey Davis did that season and you don't hear people saying he's "not a downfield threat".
I'd be a little more confident in this comparison if the mocks matched my own opinion, but overall I'm sticking with Demaryius Thomas as the best NFL comparison. All of the criticisms from that article apply to DT. He doesn't have elite speed (though his college YPR was insane), he wasn't considered a great route runner, and he doesn't have phenomenal hands. Being big and athletic matters though. JuJu athletically looks the part of an NFL #1. He's got the right kind of frame at ~ 6'1.5" 220, and he moves well for a player that size. I missed on a guy like this a few years ago (Chris Harper) who was almost too big for his own good, but JuJu's resume is quite a bit stronger.
At this point I hope people keep doubting him so I can get him in all my rookie drafts! I don't think I've ever said this before, but for once the NFL has managed to actually underrate a USC WR.