> they also still have buttons and dials everywhere. ... The reason is obvious: when you're taking photos, you don't want to be looking down at a screen
I agree that physical affordances are very useful. But I don't think the cause of DSLRs having them is because current manufacturers believe buttons have superior usability. It's because SLRs have had those same controls since before touchscreens existed and today's self-selected DSLR camera audience specifically wants products with that "vintage" user experience.
My evidence is that today's cameras generally only have hardware controls for features that existed since before the digital revolution. Purely new capabilities (like file management) have not included corresponding new hardware controls. Likewise, hardware controls that are no longer that useful, like mode selectors, are still present.
To me, this implies that camera manufacturers are not just trying to provide a "hardware control" UX, they are specifically providing "the hardware control UX of 90s SLRs".
Sure, and you could do that with an SLR from the 90s too, as I recall.
Camera manufacturers are very innovative when it comes to capabilities and new features, but incredibly conservative when it comes to user experience and form factor.