This is all well and good but the people I see on HN are ones that say that the app should actually look native on each platform, ie Material on Android etc. This opinion is what I'm pushing back on, not the fact that ctrl + C works on Windows and CMD + C works on Mac.
Of course, this is the reason why cross platform frameworks are so popular, if you're already gonna have to rewrite the UI for every platform, why not just do it once and save yourself the effort? After all, users won't care, as they've shown, because they care much more about new features coming out. There are always tradeoffs because time is finite.
> This is a big problem I've run into when doing user studies myself
Sigh, do you really think that all of these weren't considered when we did user studies? This is like 101 material, frankly almost insulting to imply that we didn't, therefore it can justify your priors, even though I agree with your points to some extent as said before.
... which you can absolutely do while using native UI controls. "Act consistently" (UI controls are in similar places and present themselves with similar UX) is not the same as "look consistently" (UI controls are drawn using whatever system theme or drawing style is in use).
Certainly there is some overlap between look & act: a platform-native "dropdown menu" looks and acts a little differently on Windows vs Android vs iOS. But I think these differences are not in the majority, and when users say they want apps to "act consistently" across platforms, you an absolutely achieve that with native UI controls, and it's not even that difficult.
This is a big problem I've run into when doing user studies myself: you need to be very precise with your language when asking users questions, and even then you often need to dig in and ask for details about what they mean by their answer. And of course having visual examples and functional mockups for users to play with helps a ton.
Another problem is the leading nature of questions you might ask during a user study: if you simply say "do you think it's better if the app acts consistently across platforms", of course users are going to say "yes". Saying "no" to that question feels kinda stupid, TBH. But if you were to give a user an iPhone and Android phone, with the same app, using native controls on both platforms, and ask them if you believe that the apps "act consistently" with each other, users are probably going to say "yes", as long as the design and UX of the apps in general are consistent with each other.
(And even that's a contrived test: very few people use both an iPhone and Android phone regularly!)