As somebody who’s daily driving the Terminal.app with ohmyzsh and never bothered switching, what are the reasons one would prefer another emulator?

The good ones are WezTerm, Ghostty, Kitty. There may be others. They are all so good that "the best" becomes subjective.

I like Warp, Ghostty, iterm2 for different reasons. And I can run multiple ones so no need to choose the best.

I used Alacritty until about 3 weeks ago, switched to Ghostty. I'm very happy with the change.