It's hard to run actual numbers on, because you have to make an arbitrary decision about which 2 WRs are good enough to even measure.
But in theory, it lowers your ceiling, but raises your floor. Tyreek and Waddle won't both have 200 yard, 3 TD days at the same time. But, it's also extremely unlikely that both WRs will have zero catches the same day.
Unfortunately, It simply doesn't seem to hold true, because it's the QB that defines the floor, and in any given week, the QB can feed a TE, WR3, RB or rush for the TD.
Tyreek Hill didn't have many bad games last year, but if you isolate weeks 3, 5, 7, 18, WC where he scored 5, 13, 14, 4, and 14 fantasy points...(all his games under 15) And then we swap to Waddle... In those same games Waddle scored 15, 5, 13, 10, 8.
Now Tyreeks best games. Week 2, 4, 6, 8, 9, 13 where he scored 42, 26, 30, 31, 27, 30 points and we swap to Waddle in those same weeks scored: 40, 6, 19, 31, 19, 2.
Basically, their ups and downs don't actually balance out, but lows still come together and highs only come together if you think Tua can repeat 500/6 on any type of regular basis.
Tua can only throw 1 ball at a time, which means statistically every time Tua throws the ball, you can guarantee one of your WR isn't getting the target, catch, or touchdown.
The chance of Tyreek and Waddle both having top 5 weeks at the same time is incredibly low. But if you draft Tyreek and... Davonta, there is nothing stopping them from both having top 5 weeks at the same time.
So if we can theoretically agree the ceiling is real, the question is does the floor exist, and is it higher than any other combo? If Tyreek has 1 catch, what are the odds Waddle also had 1 catch? Pretty low, except... Oddly enough the stats show that both players had bad weeks simultaneously multiple times, meaning that a bad week for the offense or QB tanks the floor for both WRs and doesn't seem to increase your week to week floor.
So in a game that we know we play weekly, where we agree higher variance (we believe currently) can lead to more week winning potential, then why would you want 2 WRs on the same team? Because as we've talked about elsewhere, even if you have Waddle projected with more points than D.Smith, it's HOW and WHEN you score those points that matters. If Waddle only scores well on the weeks your #1 WR has down weeks, does it benefit your team? Whereas D.Smith has zero correlation of good\bad games to your WR1, so no ceiling, and an unknown floor that are unrelated.
It's really no different than RB committees. Maybe D.Mont and Gibbs both have top 12 seasons, but when you visualize how and when they will both score their points, owning/starting them both on a weekly basis, doesn't seem to be enjoyable, because only 1 of them is getting the TD per drive.
If the Lions only score 3 TDs in a week, your maximum TD total is 3. But if you own Gibbs and Bijan where ATL also scores 3 TD, your maximum TD total is now 6 from the same 2 positions on your roster. BUT it also increases the chance (on paper) of 0 TDs from either.
I employ this strategy with QB and Kicker. Because when the QB is scoring TDs, the kicker is only getting 1 points. When my kicker is getting 15 points, it's because the QB never got in the end zone. One offers an assumed floor, the other offers a higher ceiling.
Just remember, we're not talking about dropping players entire tiers or DND, we're only thinking of, well I have Waddle WR10, and Smith WR11, since I have Tyreek, I'll go Smith. No one should be doing mental gymnastics to drop players or adjust rankings, I would only use this is a tie breaker between players within the same tier.
Chase's best Week, Score, and Higgins score that same week:
7: 33 - 14
6: 32 - 11
1: 29 - 5
14: 29 - DNP
18: 23 - 2
WC: 23 - 7
DP: 17 - 6
Now let's go the opposite direction, Higgins best week, Score, and Chase score that same week:
16: 27 - 16
11: 24 - DNP
12: 24 - DNP
4: 25 - 12
CC: 21 - 13
2: 19 - 11
Every time Chase had a good game, Higgins scored less than 15 or Did Not Play.
Every time Higgins had a good game, Chase scored 16 or less, or DNP.
If you want to argue the "floor" I'm actually inclined to believe it. On paper it makes perfect sense to me. For these 2 WR it seems to be somewhat true, maybe because Burrow never COMPLETELY ****s the bed, whereas Tua...
But, for the moment, all I'm trying to provide is proof of concept, that the "ceiling" exists when you draft 2 WRs on the same team. We can argue the impact of that ceiling, if it even matters, we can argue whether the floor is a valuable enough benefit to counter the ceiling cap, whatever we want to do from here.
My only goal was to provide proof of concept, that 2 WR on the same team, does in fact (well, given our tiny sample size) appear to come at the expense of one another on any given week.
Higgins is more valuable when Chase doesn't play. That doesn't seem crazy to say. So it shouldn't be a hot take, to imply that owning Higgins AND Chase limits your potential ceiling on any given week.
How much that matters is up to each individual to decide, but I think it's a fallacy to imply it doesn't matter or has no effect or shouldn't even be considered or that it's some crazy complex concept.
Chase averaged 20.5ppg, Higgins averaged 13.7ppg. There is not a single week, in which both WRs scored equal to or above their own personal averaged. 3 of their best games all season, came when the other one wasn't on the field.