I've recently stopped using tmux in favour of relying fully kitty's built-in windows and tabs, and I'm a fan.
The real killer app for me was the "pass_keys" plugin that allows you to navigate vim and kitty splits all with the same keys. I think there are plugins that allow you to do the same between vim<>tmux<>kitty as well, so it's not like you would need to drop tmux to take advantage of it.
Anyway, so that's been a big shift in my daily workflow. I've been using tmux for well over a decade, and GNU screen before that (I was never able to train myself away from the C-a prefix.
The one thing I miss a lot is being able to quickly detach and re-attach to existing sessions. Especially when doing some work over an ssh connection. But then I can always just shove the terminal into scratch space, or another i3 workspace.
This isn't me trying to sell anyone on ditching tmux. I love tmux, and if it works for your flow then it's perfect for you. More just curious what kinds of setup other people have.
Is there some hot new thing that I've missed that blows both kitty and tmux and i3 out of the water? Idk, but I'm always on the lookout. :p