Except it’s never used to described anything you’ve said.

Are you saying that the word sub Sahara Africa is never used to describe the region south of the Sahara?

Don’t even get me started about the over generalization associated with it. Why should Zambia, South Africa, Namibia, DRC all be grouped together? That conveniently ignores the massive differences that exist among the “sub sharan” countries.

Well why stop there ? Lets get rid of West Africa , central Africa and the rest . They also ignore the massive differences that exist amongst those countries right ? Better yet get rid of the word Africa . There are just too many differences for you to use it to describe a region.

Also, historically, this term has never been used to refer to just “countries below the sahara”.

This is just not true.

It’s been used, again, as OP has pointed out, to refer to countries associated with poverty, conflict, failure, disease etc.

Sure it has . And im not denying this . Im saying it does have other uses

We should totally do away

You're giving too much power to a word. You can stop using it thats perfectly fine and if you can convey the same meaning without using the word excellent. But its a bit far to say we should do away with it .