The delay is certainly frustrating. I use a patched version of kitty terminal that moves starship prompt to the bottom of the window, similar to vim and emacs. Since modeline updates are asynchronous, the shell prompt is very snappy even in big git repos. The downside is that you have to patch kitty and I never bothered to test my personal pet project on anything else than Linux.

https://github.com/mbachry/kitty-modeline