I agree it should be easy for newbies. For exactly the same reasons you stated.
But when that equation goes threw my brain it computes a different answer.
The answer would be latest as the default page(clearly labeled as such). And with “categories” clearly and easily there.
I think most websites work like that. From newspapers to blogs to blah blah.
Front page is latest stuff and if you want to look further it’s obvious and clear how to. You start looking for categories.
Joining and coming to grips with all these new systems and log ins and people and categories can be overwhelming. In my mind it’s better to see what’s topical and if you think aha I need to check xyz you naturally look for categories like you would on newspaper site etc.
I think the way “unread” is accessed however is different by definition (actuality) for new people and regulars.
“Unread” for people who have been here a long time is like an email inbox. Presuming you’ve read everything you only see new stuff. For people who have been reading all articles since day one this is useful to show what’s just come in or I’m probably not going to read because it’s a topic I’m not interested in.
“Unread” for new people means something slightly different. is a list of all unread items since joining. If you’ve just joined that’s everything. And highlights what you need to look at yo get familiar with the different topics.
For this inconsistency in what unread implies to different people I would say use it as a secondary way to navigate.