They are overrated because they don't have a proven real elite #1 WR. Lots of good pieces.
Before anyone jumps on me, yes, Fields is damn good - but he hasn't been great in big games, and due to injury or something else, the WR corp wasn't awesome down the stretch last year and struggled to get open against elite defenses aside from 1 quarter against Michigan. USC, UW, not much there. IIRC they did ok against Utah.
What I'm saying is that they are a really good corp with a lot of depth, but that to be a top 5 unit, there has to be some real cream there. Is Fields a first round draft pick, or even a 2d round pick?