Like many other people, I use oh-my-zsh for default setup and that's it. I literally use a single plugin for git and very actively autoload my custom functions to avoid startup delay. With my 384 line config and oh-my-zsh on, here are the results:
$ hyperfine -N "zsh -lc 'exit 0'" "zsh -c 'exit 0'"
Benchmark 1: zsh -lc 'exit 0'
Time (mean ± σ): 54.5 ms ± 6.3 ms [User: 10.2 ms, System: 14.3 ms]
Range (min … max): 38.1 ms … 64.9 ms 78 runs
Benchmark 2: zsh -c 'exit 0'
Time (mean ± σ): 6.5 ms ± 1.4 ms [User: 0.8 ms, System: 1.3 ms]
Range (min … max): 3.9 ms … 14.2 ms 424 runs
It's crazy how their startup time is 380 ms, and I suspect something else might be the reason, not just oh-my-zsh
$ hyperfine -N "zsh -lc 'exit 0'" "zsh -c 'exit 0'"
Benchmark 1: zsh -lc 'exit 0'
Benchmark 2: zsh -c 'exit 0' It's crazy how their startup time is 380 ms, and I suspect something else might be the reason, not just oh-my-zsh