I read the title and my jaw dropped. Your QB doesn't change how crisply you run your routes. It doesn't change how you shake off defenders. In short, the QB doesn't do the receiver's job before the throw. The QB's job is to throw to the open man in a spot where only the receiver can make a play. If the guy isn't open, no QB is getting him the ball.
Evaluating an NFL QB has always been about how well he can execute the offense. In the NFL, compared to college, the reads have to be quicker, the accuracy greater. Why? Look at some of the top players in college over the years that have flamed out in the NFL. When your guys are wide open because you have talent stacked on one team, the QB can be slower to process his reads because the OL is creating a solid pocket. The QB doesn't have to be as accurate because sheer athletic ability gets his WRs open. The QB can take off and run because his athletic ability is greater than his competition.
Heading to the NFL, most of that disappears. The defenders are all fast and strong. Even some of our most miserable NFL defenders were, at one time, heralded college athletes. So even the best OLs can't protect the QB as long, speeding up their reads and placement decisions. WRs have to be precise in their routes, have subtle movements to throw defenders offline, and create separation. Running QBs are getting hit more often.
This further exacerbates the need to look for QBs who can make quick reads and know how to cycle through their progressions. In college, their elite WRs are just open almost immediately, eliminating the need for checkdowns, which are vital in the pro game.
It also explains why so many top WRs fail to make an impact and you end up with non-first rounders making an impact. They tend to be the guys who don't blow by people, but who run great routes. Look at our history of drafting WRs in the BB era. The impact guys are never first rounders or the speed guys. Branch, Brown, Edelman... even guys like Welker fit that profile.
In short, WRs absolutely can be evaluated absent solid QB play