I'd want to see some actual hard evidence before I believed that. The usual way social cues work is they are devastatingly effective even if people claim they are not. Much like how most interviewers are honestly convinced that their approach is unbiased but in practice they tend to hire people who are like themselves.
My expectation is that turning up in a suit would get better results. The effect is probably smaller in hard-skill roles but I'd assume still present.
I agree, but I suspect that you’d have much better luck if you wore something that was superficially similar to the kinds of things other people wore, but was much better fitted and higher quality. For instance, if you showed up in a nice pair of chinos and a tailored buttoned shirt (of appropriate formality), that might come across as being really put together rather than ignoring subtle social cues by dressing in something that stands out by not fitting in.
I don't know where you live but for most tech jobs here even outside of sv its almost as bad as putting your photo on a resume. Even for very senior non-technical roles you're better off showing up in slacks and a blazer than the whole enchilada
Wearing a suit to a tech interview in silicon valley would without a doubt send the signal that either (a) they have absolutely no clue about SV work culture, or (b) they’re a “look at me” guy who dresses odd on purpose
If they're young it can also be because that's what they've been told to do, if they're from a different culture (even an American one) it may be shockingly weird not to wear a suit to an interview, and there are even people who wear suits all the time because a well-made suit is very comfortable, with no more showing off involved than dressing up any other way. An interview is not a regular work day, best not to summarily judge people like that.
My point is that even knowing the work culture of SV does not mean that people necessarily believe it applies to interviews too, or that a suit will be a negative point, rather than good or neutral. There is a strong culture of looking smart at interviews that overrides knowledge of day-to-day attire. If you really care about people being in casual clothes, mention it in the invite, rather than looking down on them for doing what has been ingrained to be appropriate.
My expectation is that turning up in a suit would get better results. The effect is probably smaller in hard-skill roles but I'd assume still present.