IMO, QJ is going to take a couple years of being an NFL WR to "get it" like Golden Tate did, and then only *start* to "pop" in Year 3, and truly emerge in Year 4. I do think he'll become a good pro, Pro Bowl level. Meanwhile, JSN will be ready to start and play at an NFL level from day 1, and only get better from there.
Assuming QJ does develop as a good NFL receiver, by year 4 the two *could* have comparable value to their respective teams. However, we get three more "good" years out of JSN's rookie contract than we would have gotten out of QJ. Let's say JSN shows enough the team picks up the 5th year option, and that year 5 is also a comparative bargain. (Especially with Lockett probably retired)
JSN's earlier NFL-readiness could be the difference between a playoff win or playoff loss a couple times in the next 3 years, e.g., by having JSN we convert that key 3rd down at crunch time and help the team over the hump to a playoff victory. After all, what if Kearse had caught that 3rd down pass in SB49 that could have put us in FG range and burned clock? In that hypothetical, JSN would have both gotten more separation and also made the catch, drive continues. Lockett, DK, JSN, our TEs, how's the opposing D gonna cover them all?