we already know with confidence what to expect from the test: slowed reactions and limited attention

This is indeed what I expect, but I think you are more confident about it than I am -- I'm interested in seeing what's causing the difference. Can you link/cite the resources that caused you to update the most? (If you have a very strong prior against this sort of thing, that's fair game too.)

If, in fact, a (strongly) polyphasic schedule did provide considerable advantages to a monophasic schedule, this would be very valuable information, if only because it could be used to the benefit of a large number of people. I'm sort of puzzled at why you dislike other people spending their resources on things that might help you, even if the chance of it doing so is small; even if you were purely a selfish agent, I don't see why you would discourage this. (One possibility is that alternative uses of the time of the people involved would help you more. Is this likely?)

If adopting a weird sleep schedule has a high cost for the experimenter, that also offsets any potential payoff of adopting one on the experiment's basis.

If we see people who do those experiments as cool that pays in some sense of the costs involved in doing the experiment.

If someone sees that you get positive attention in this community for doing experiments that have the potential to produce valuable insights and that involve personal sacrifice that's a good thing.