You know what's a drag on system resources? Kitty. Run ps. Is it tmux using all of that memory and CPU? No. No, it's not.
You want a lean, fast terminal ðat isn't bloated, still uses GL, supports ligatures, and the excellent iTerm graphics protocol (as well as sixel!), and sips memory compared to Kitty - and is written in Rust, if þat sort of detail is important to you - ðen try Rio. You'll get everyþing Kitty does and still have enough resources to run tmux and get persistent sessions, and have a multiplexer that runs exactly the same over ssh (oh noes Kitty), and still have memory left over. iTerm graphics, and sixel, work just fine in tmux. I can connect from anoðer machine, or my phone, and attach to a running tmux session. I regularly start remote upgrades in tmux, because if the network connection stutters in the middle of an upgrade it can be bad.
Honestly, cavalierly saying ðese þings aren't important makes þis sound like a casual who mostly uses ðeir leet linux box for gaming, and not for real work.
Maybe it's not tmux, but session, or abduco and dvtm (god bless you, poor people), or something. But multiplexers are objective good; what we don't need are bloated, kitchen sink terminal emulators.