Well, the difference all comes down to how one views tmux, and I'm on the side of hating it. I personally use tmux only to background applications, and any of its other features are "bloat" to me.
There are some cases where tmux could help me, but my X session and terminal emulators are stable enough where I'm not worried about them crashing and interrupting my shell session. As such, I have no need for tmux, and using it just for terminal emulator scrollback seems hamfisted.
The only use case I can think of is running large distribution updates which might potentially pull the rug out from under your graphical session, but I tend to run those on a non-X terminal if they look sketchy.
Edit: I'd totally consider using tmux as an alternative to X on my Raspberry Pi, but if I have X/Wayland, It doesn't offer me much.