Most of can’t use Facebook. They can read and send, nothing more. They can’t even change order of showed comments.
One small forgotten detail too 
Do they need more? Quite often no. And that is the only strength of Facebook — they show only essential ones. And the strongest weaknesses are that fact there isn’t anything more.
The difficultiness (is that even a word) comes from demand to understand markdown and remember lot of different things. Sorry to say this at loud, but sometimes I have a feeling that Discouse is planned from devs to devs.
But I have to say that Discourse is changing to more… john and jane doe -friendly direction.
There is responsibility of admins too. Is it really necessary install all bells and whistles? Are those tricks really to users or are those there just because an admin likes and events are for marketing?
So, it depends. I would do a different forum for knitting than for SEO-marketing and for state-of-the art devs.
And for that we need easy to use ability to hide and show different tools and things based on groups. Some we can already do and others need dev-skills.
Would that make admin’s life easier? Defenetly not, because then there would be hell of settings. But perhaps that is one part of admin’s work?
Should I pinpoint where are difficult parts when we are talking about ordinary facebook level users? Yeah, I should because otherwise this is just another meta BS post. But I’ll wait easy tool to adjust composer toolbox first, because that is the very first issue of easyness of lesser skill end-user 