I'm not entirely sure I can decipher this, but I'll take a stab at it.
Yes, Cooper has been very good (and at times fantastic) and elevated this offense from mediocre to great.
If you do a modicum of research you'll find that generally Cooper's "inconsistencies" was by and large a product of Garrett's tendency to go into a conservative shell on the road - Cooper's numbers have otherwise been pretty consistent before and after Garrett.
Also, I don't see much evidence that Cooper isn't our best WR currently. If you have evidence to the contrary I'd love to see it. Antecdotally, Cooper for instance sure looked like our best WR in our most recent game - Lamb was plagued by drops and Gallup was invisible.
The point, however, isn't specifically about Cooper, but rather that having THREE WRs of the caliber that we have is incredibly difficult for defenses to handle. Exponentially more so than 2. I wouldn't give that up for anything short of an outstanding deal. You have to weigh any potential deal against how much it can actually, legitimately help you in other areas. Because dealing any of the three, at the moment since only one of them is getting paid, takes a lot away from one of our prime advantages against just about every team in the league.