Here is how to reproduce it.
Ssh to a system with tmux. Attach to tmux and "head -100000 maillog" or whatever big. Measure how long till it's finished. Try to switch to another tmux window and back while it's going.
Repeat the above in another terminal and compare.
Windows Terminal is actually pretty bad under tmux but ok-ish without. Can't switch off to another tmux window while it's going either so basically locked in. That's unusable.
The argument could be made that tmux is an issue. But since 100% of my ssh is under remote tmux and it's fast in putty/kitty I can only blame other terminals. Even without tmux kitty is 2x faster than windows terminal. And kitty doesn't slow down under tmux.
Repeat the above in another terminal and compare.
Windows Terminal is actually pretty bad under tmux but ok-ish without. Can't switch off to another tmux window while it's going either so basically locked in. That's unusable.
The argument could be made that tmux is an issue. But since 100% of my ssh is under remote tmux and it's fast in putty/kitty I can only blame other terminals. Even without tmux kitty is 2x faster than windows terminal. And kitty doesn't slow down under tmux.