Their are 10-12 LB rated to go in the 4th and 5th round. I see that as a bigger need then WR.
Anything passed the first round or two is almost always BPA. If the staff has a WR as the BPA, then so be it.
Plus, OP didn't say who was or wasn't already off the board. If most of those LBs with 4th round grades you mentioned are off the board, which I am assuming based on his mock, then I have no problem with a WR.