My terminal (terminator) does (2) and the "easy" scrollback on tmux messes up the ability to scroll with the mouse, at least with default settings. I just tried it in zellij and that doesn't. Since I'm only using a multiplexor for (3) and zellij does that too, I'm already inclined to switch.

I know I'd get used to them, but the key combos used by tmux seem very odd choices, even to someone who used to code on a real glass tty!