Then why don't scientists do that for every single experiment? It's better to assume that god and luck don't exist and be done with it
God just doesn't really matter for most experiments, so we don't need to account for his existence.
As for luck it generally gets compensated with large sample sizes.
Besides that, Some studies point out that the placebo effect doesn't even exist. How do you relate that to this chapter?
As for the first article you reference (I only read the abstract). It seems to be mostly about how the placebo effect is overrated and that a drug should do more than just barely beating the "placebo effect".
It also says: "The fact is people heal and that inherent healing capacity is both powerful and influenced by mental, social, and contextual factors that are embedded in every medical encounter since the idea of treatment began". Which clearly would include an encounter with a placebo pill.
As for the second article (here a link to the original article it was presumably based on
https://www.nejm.org/doi/full/10.1056/NEJM200105243442106)
It does say it is insignificant for most studies, but with an exception for subjective effects, like on pain.
As for how the chapter handles it I think it does quite well. I think it makes it clear enough that it doesn't actually improve your luck it just makes you perceive your "luck" more.