I think there is this assumption that 'good UX' and 'good onboarding' actually means preventing new users from learning anything, for that only implies confusion and friction.

This notion IS true, but only for the idiot masses. And however much we want it to be the case, those will not get onto Nostr anytime soon. There are many many many many maaaaaany millions of non idiots that are more than capable and willing to do the basic learning. Those people are far more likely to get onto Nostr. I like to look at the population numbers of the Roman republic to conclude you don't need that many people to be meaningfull.

Subsequently, once all of those people are on Nostr, and the idiots come, those idiots can ask their nephew for help when things go wrong.

I.e. get the nephews first. "Mass addoption" is putting the cart before the horse.