Fine, he's Keyshawn Johnson. A receiver archetype that last saw its heyday 2 decades ago. Those types of receivers do not succeed in the modern NFL. You still need to separate if you're tall. Jump balls aren't an offensive plan. It's like 2000s basketball, iso your one good player, and clear everyone out to the other side.
Outside of *maybe* Mike Evans, although he's become a much better route runner in the NFL and always got separation (because he had to with Johnny Manziel in college), name me the slow, jump ball, """"route runner"""" (McMillan's route-running is fine, not great, certainly not top-5 worthy) that's succeeded in the league in the last 10-15 years.
Teams talk themselves into this kind of receiver every year, and yes, the Patriots talked themselves into N'Keal Harry (although at least that was pick 32). And the success rate is incredibly low. Much lower than the undersized fast guy archetype (McConkey).
It's pick 4. If it were pick 24, I would maybe start to consider it, but it's not. 4 is generational-type talent, or trade down. That's it. Settling for a mid-to-low-first round talent (McMillan, Campbell, Carter) would be a disaster.