Well you can't assume that a crop will end up being good.
We've sat back before a college season before and said "Six QBs might go in the first round next year" only to have two go in the first round. I think you fill roster weaknesses as you can, and if you are always waiting until next year to fill major holes, you'll end up sucking more often than not.
McBride looked pretty good by the end of the year and both Cam Thomas and Myjai Sanders looked to be at least rotational quality edge. I'd argue that you want more than just two edge players if you really want to rush the passer consistently. I always liked how the Giants used to have like 4-5 guys who could rush the passer on their roster at all times.