I had really started to feel it slow down lately. It hit the breaking point when I was cmd-tab-ing and found myself waiting for more than a second just for the terminal to appear.
Looked around, evaluated a couple alternatives and none of them quite fit my taste. One terminal required an account/login to operate, which is a big no IMO, another was written in {Java,Type}Script so simple commands like `yes` would break it due to the async nature of streams in node.js.
I really like WezTerm so far. It's quite fast, very much configurable and comes with the theme I was configuring with iTerm2 out of the box (OneDark (base16)).
My only trouble with it was in the beginning when I had to add the configs for cmd-left and cmd-right in lua config, I really hoped they'd be in there with the defaults.