Yes I do

That's not the only function

it is also used to update grapheneOS apps. (I know it is a simple appstore)

I just said "you don't have to install it" because I 'felt' that you thought it is necessary to do so.

you only need the sandboxed googleplay services If you use apps that require it. (most apps on google play store)

A better way to do this is using multiple user profile (ex: one for banking and personal stuff with google services and another profile without it but you only use free / opensource apps)(user profiles are like a another phone but easier)*

and the whole point of sandboxing googleplay services is that you don't need a replacement.

Hey, where are you?

Sorry if I have overwhelmed you.