I'll say this about WR, there are ways around replacing Pickens that doesn't include a first round pick or spending 20-25/year on a guy like Parker Washington.
The WR class is pretty deep and you could easily get a round 2 guy who could push Flournoy to be the WR2 as a rookie.
The issue is that you can't just roll with Lamb, Flournoy, Williams, Ferguson, Spann-Ford, and whatever slop spare RB2 you pluck off the scrap heap as your skill position players, plus a 2nd round rookie. If you want to do that you're basically going to have to earmark your 1st rounder for WR if you want any sort of serious skill position talent around Dak in his last 2-3 years.
To avoid doing that you'd need to sign a starter-level RB alongside Williams to make the running game more dynamic, and then off that cobble together production in the passing game opposite of Lamb with Flournoy and a 2nd rounder.
The issue of course is that Steele is still a piece of shit at RT and the defense is obviously in need of talent basically everywhere, so I'm not overly thrilled with the idea of having to take a WR in the 1st/2nd come hell or high water.