Some data in support of @soraminazuki (who makes good points throughout this thread) on an i7-1370P linux laptop running Linux 6.15.7:

    $ tim 'bash -lic logout' 'zsh -lic logout'
    55.3 +- 3.7 μs  (AlreadySubtracted)Overhead
    7454 +- 26 μs   bash -lic logout
    7934 +- 39 μs   zsh -lic logout

(Using https://github.com/c-blake/bu/blob/main/doc/tim.md)

About 20,000 entries in the Zsh history slowing it a little. All completion activated (but zcompile'd, along with a very large digraphs.zwc).

I think most would not be troubled by taking 1.06X longer, though, especially at this 8 ms scale and for interactive session initiation. Note this test upper bounds Time To First Prompt { a different "TTFP" from Time To First Plot ;-) }, since it also exits as part of the `-c`.