It also says that both of them are limited by tmux, which I use 100% of the time in the terminal. The real problem is when you run Vim in tmux and start to scroll in a large file that you notice that Terminal.app does not cut it. It lags badly. In Alacritty its silky smooth.

And yes, scrolling with j/k for longer periods may be an anti-pattern in Vim and yada yada... I scroll in Vim, and in Alacritty its smooth, in Terminal.app its sluggish.