I use vim because its got :sp/:vsp, can edit remote files over scp, :E, :earlier, and now :term, plus so many options in vimrc. I don't think I really even need tmux w/ it anymore.
The Vim author was against adding :term but their hand was forced by the success of neovim from what I understand.
i stopped using tmux because now all i need to do is open a terminal buffer in a new split to multiplex. i rarely used it for sessions, but use abduco[1] for that now when i find the need.
In other words, screen handles persistance and the ability to reattach to an existing session. The outer vim serves as a terminal manager. The nested vim instances are used to edit code, etc.
I think it's actually more likely to be useful for you (or anyone) to get intrigued, fire up vim, and use, say, `:help :term`. At least, that's what I'm off to do!