If your hardware cost is driven by the performance of your shell, I question what you're doing with your terminal emulator.
I can think of essentially zero areas in which zsh is slower than bash in which it is slow enough to create the need for a hardware upgrade, or even contribute to such a need on an already-overloaded system. I mean, sure, file performance bugs if you want.
But your shell is not going to be the "oh christ, this is slow" program; it doesn't run Electron for chrissakes.
Git completion is unbearably slow for me in zsh, but fine in bash. It is a very large repo I work on, but we're talking 10s vs instant. I still use zsh though because it's nicer in other ways.
Check your Zsh theme. Zsh has no built-in support for git status, so themes that show git status are implementing this by themselves. One way to make this slow is to check git status synchronous, however there are ways to do this asynchronous that should be instantaneous (at the expense of showing git status later).
Btw, Bash is the same. So you just said that someone that implemented your Bash theme did better than in your Zsh theme.
There are absolutely some things slower in zsh/bash. Are any of those slow because of a non-upgraded machine ("they would run fast on a $50k server" doesn't count)? Or, as others in this thread have pointed out, are they slower because of flawed implementations which, unless fixed, will always be slow on any hardware?
