I'm against this for several reasons. First, WR was certainly one of the reasons we lost to KC, but the biggest is that our back 7 was abysmal (and our front 4 only slightly less so). Your proposed scenario unequivocally makes our back 7 even worse. Dodson is not a starting MLB. Elam is better than Dane Jackson and should have been on the field over him against KC.
Second, our cap situation is in a very dire spot and we can't wriggle out of it by restructuring Diggs' or Miller's contract. This needs to be a year where we draft as many players as possible and start more of them than McDermott is usually comfortable with. I would expect rookies at WR, C, DE, DT, and/or S to get ample playing time. As far as I can tell that's the only way we're going to have a starting caliber roster. I read through your whole discussion and I agree with what you say about depth being less important, but I'm talking about starters.
Third, I agree we need more elite players. That is why we need to draft as many players as possible, to give ourselves more chances. Here are the Chiefs' elite players (other than Mahomes) and where they were drafted:
Kelce - 63rd
Jones - 37th
Sneed - 138th
Humphrey - 63rd
Thuney - 78th (by the Pats)
Their two recent foundational drafts happened because they collected picks after trading away an elite player.
Also it's possible Bernard will become an elite player next year. I think there's even a slight chance Elam becomes one at some point given his penchant for interceptions.
So no I would not actively make critical spots on the roster worse, and reduce our chance of finding multiple elite players this year and next, and take a couple of high-upside players off of our roster, just for one WR no matter how good his prospects are. Instead I would stick to the plan of drafting a WR at pick 28 and taking another one in rounds 2-4.
I also don't agree when you say there's no use trying to stop KC in the playoffs. That we just need to beat them in a shootout and there's no other way. This is the biggest myth I see posted on this board all the time. KC has in fact been stopped in the playoffs. Just this year the Ravens defense held them to 17 points with one streak of 6 consecutive drives that ended in punts, and the only reason that defensive effort was wasted was because of a couple goofy turnovers in the red zone. Don't let our defense, and that means players and coaches, off the hook. Certainly our offense could have been better, most notably the WRs. But you know we once had a WR rack up 200 yards and 4 TDs against them and that still wasn't enough to overcome an abysmal defensive showing. So at some point the defense simply needs to show up in the playoffs and we're not going to see that happen if we trade away one of our best defensive players.
We're only having this discussion because Beane has yet to find ONE elite player with one of his original draft picks, and McDermott has yet to coach ONE proper defensive showing against a good opponent in the playoffs. So I get that the fanbase is grasping for any conceivable means of overcoming the Chiefs in the playoffs, but the simple reality is that one or both of those men need to do better at their jobs, or else they need to be replaced. That's the only way we're going to get over the hump.