This. I used to have that setup (Prezto + Powerlevel9k) but in the end I didn't want all sorts of needless config, and it still felt really heavy. Plus, you actually rarely use anything in the framework.

Now I just use zsh + zplug (vim-plug like plugin manager) + pure zsh theme + tiny zshrc. Fast as hell, tailor-made and no-nonsense. You can check it out over here if you're interested: https://github.com/jorvi/dotfiles