It's more like they're paying him like a top-20 WR because the guys just below him are getting paid pretty similar dollars to what he is (if you want to argue DJ getting $20m is meaningfully different than Kirk getting $18m, have at it).

And most people consider it a slight bargain contract because its front-loaded and his base amount drops every year from now on. And because WR is highly valued these days - you can see that in the draft and in the contracts guys are getting.