You'll have to show me where anybody has said the bolded. That kind of hyperbole/extrapolation makes discussion difficult. Watkins is an extremely talented player. I don't think anybody disputes that. Certainly more talented then Kupp. The problem is, at this point, he is unrealized talent.
No, stats sheets do not show a players entire value. Of course not. However, you cannot simply ignore them at a position like WR. Do you really believe the Rams thought they were trading for a field spacer/coverage eater with little production? Nobody values that at a 2nd round pick +. Great, he draws a double team most of the time. So does the #1 receiver on every team in football. Why does he have so much trouble producing vs other top WR's? A top WR talent produces, regardless of coverage. That's a fact. Do OBJ/Evans/Brown/a dozen other #1 WR not face these impenetrable defences?
He might still reach his potential but it's perfectly fair to wonder if it will ever happen. Every year that passes it becomes less likely. At this point, outside of about a 10 game stretch, he's been no more than average over a 4 year career. 4 years is not a small sample size.