I'm not concerned about him. As far as chemistry with Geno vs Lock.....he had two passes thrown to him downfield when Lock was in. One of them hit him in the hands and he wasn't able to pull it in (I remember it as a 'tough but catchable' ball), and on the other the ball wasn't anywhere near him. It was clear that he wasn't where Lock expected him to be - whether he or Lock made the error is not something that we'd know without knowing the playcall.
People have mentioned Bobo; JSN has a considerably higher snap count but I think it has gotten closer as Bobo is a better blocker and we've needed it.
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I've been a little frustrated with the screen passes to JSN (someone mentioned the Eskridge plays and I think that's probably accurate), but I see him as the replacement for Lockett. Tyler has clearly been thinking about life and career post-football. I wouldn't be shocked if he retired after any given year - could be this year, could be next. I think JSN will slide right into that position in the offense.
I don't expect WR3 to be getting a ton of catches so that doesn't worry me, but I'd love to see more of what I was expecting when he was drafted - that 7-15 yard range with a chance for some YAC.