I recently switched from iTerm2 to Alacritty https://github.com/jwilm/alacritty. It does not have scrollback, splits, tabs and other fancy features. But for me, performance and snappiness is the most important feature (besides, I use Tmux for all those things mentioned).

For getting something close to i3 (you wont...?) on macOS I am using chunkwm https://github.com/koekeishiya/chunkwm.

I spent some time during the summer to get to know Linux using i3 (i3-gaps actually) with urxvt on a VirtualBox. I do recommend it!