(Not a dev, just another end user.)
It could also be in my case that I use it so little that some latency is tolerable. I don't develop interactively in zellij or tmux. I mainly keep some logs tailing, and DB consoles open, etc, and I don't check them super often.
In screen & tmux you can also use vim shortcuts to navigate the scrollback buffer. That is so convenient and makes me work so fast. I can search for a snippet close to where I want to copy some text, and then navigate more precisely with the vim shortcuts.
So that's the first thing I look for in a terminal multiplexer, because if you're gonna expect that I'm gonna put my right hand off the keyboard and use the MOUSE to awkwardly select some text in a TERMINAL, then you expected wrong.
If you're interested I can share my config.