It figures that a fancy terminal emulator developer would take issue with tmux.

Tmux undoes all the fancy performance end ergonomic stuff they spent their time and energy developing. Moving stuff to the GPU, multithreading, etc. -- all just to call tmux anyway and lose 100% of those features!

What we really need is a protocol for tmux (or other terminal multiplexers) to expose its internal state to native terminal emulators so that you can get the best of both worlds. That's a tremendous amount of work, though.