The tough thing about matching up wideouts and cornerbacks is that the offense is going to do whatever they must to move the ball as well as they can. That can mean that the WR stays in place and others fill in with more work for that game. It could mean that they will move the WR around the formation. The top WR will move all over. That makes it harder to track where they might play.
By the same token, the defense is committed to stopping whatever the offense is doing. That may mean leaving a "natural" matchup alone (meaning RCB matches on LWR, LCB on the RWR) or in some cases committing a shutdown guy (Josh Norman, Aqib Talib, Janoris Jenkins, etc) onto a WR no matter where he goes. Sometimes they will tell you that in advance. Sometimes they will not tell you. Sometimes they tell you but they are lying (go figure). And sometimes one or the other gets hurt and it doesn't matter.
When I approach projecting for a player, I consider it always in the context of that individual game and for RB and QB, I will consider the opposing defense as an entire unit. A defense is a sort of organic, reactive thing. That an opposing defense has a great DT or LB is great for them, but it just means the offense is going to work around them if it is a problem. So matching up QB and RB (and really TE) is more a matter of how the offense uses that particular player compared to what the opposing defense as a whole generally does (keeping this kinda simplistic).
WR is a different animal than any other offensive position. First off, they run down the field into the heart of a defense and catch a ball with no blockers (Patriot pick plays notwithstanding). If one guy on your team is a headcase and an egomaniac, make him a #1 WR because he has to be fearless and full of too much confidence to realize he is going to be killed on most plays.
They are also the only position that often is tackled by just one player who was committed to defending him and that was running along with him. Safeties will come over and help usually but the most important part of the WR job is run downfield and catch the ball at the exact point the QB assumes you will be. If you run after the catch, all the better. But Job #1 is get open, at the right spot, and catch it.
The most predictive relationship between a defense and an offensive player is the WR-CB pairing so long as neither side deviates from where the receiver and cornerback naturally line up.
Bringing all this back where we started, I track the top cornerbacks and Claiborne is above average. He's been better than RCB Buster Skrines. They could move Parker around but so far they don't usually. Kenny Stills takes the traditional deep routes on the other side. Jarvis Landry in the slot tends to play the possession role in the middle of the field. You see WR movement much more when there is an elite WR and the rest are not nearly as good. Think AJ Green, Dez Bryant, Antonio Brown, etc. But Parker isn't in that class yet.
It only takes one broken play for a WR to get a 90-yard TD. And you have to factor in what the rest of the offense is likely to do. Giving this much time to this means I am probably guaranteed to be wrong. I may be wrong, but I can usually explain why.