He probaly means tiling window manager specifically, which makes tmux's binary partitioning redundant for all but remote work.

I used to use tmux much more heavily locally before I switched to a tiling window manager, now I only use it when I need to do a lot of work over SSH or am using an unstable connection or long running process etc.

I get you.

Since I moved exclusively to i3 some 10 years ago, I find myself seldomly using screen/tmux anymore.

The splitting, moving and switching of windows is just more convenient. Tmux has been relegated to start long running processes on remote servers, and remote pair programming sessions.

I could see myself using tmux more if I could find a way to get a more seemless experience when having to scroll panes, copy/paste, handle $TERM properly with vim (I always end up with partially refreshing vim colors under tmux), etc

the main advantage for tmux is in remote use. i work on multiple machines (laptop, desktop, etc) and i often like to access one from the other. tmux allows me to switch devices in a seamless way. i don't use i3 but you are right about the splitting in particular. it would be nice if we could have more gui integration of tmux. like a graphical tmux client that maps split windows to resizeable gui panes