My thoughts on why a WR is NOT a huge need.

Because we had no one else to do so. I'm curious as to why Carr didn't pan out? He had the measurables, but was rarely targeted, etc.
Michael Thomas doesn't line up in the slot because no one can't. He lines up there because Payton is aggressive at trying to find mismatches. You will see a lot of plays this year with both Thomas and Sanders in the slots with Tre'Quan and Hill/Harris on the boundaries.