I don't have an issue with dropping Cobb for him. Packers are like the Saints, going to spread the ball around so much that Cobb is going to be hard to trust every single week. We know what Cobb's ceiling is at this point, he's 3rd in line behind Nelson and Adams. Pryor has #1 potential on his own team. I think he's just starting slow and still working on building chemistry with Cousins, but you saw in Week 1 Pryor was targeted 11 times. Week 2 (4 targets) was sort of an anomaly, and they throttled Oakland so bad in Week 3 that he didn't need to be fed a ton (only 4 targets as well). Cousins is also a bit of a slow starter in the past also, I'm banking on both of them picking it up, BUT they face KC this week and bye in Week 5, so it might take another 2 weeks to start seeing it.
Cobb becomes much more valuable if Nelson or Adams miss time, and is on the better offense of course. With already having AB, Landry, and Sanders on your roster, I'd be inclined to take the lottery ticket on Pryor since even if Cobb moves up to the #2 you're not likely to start him much.