I can see that you are not happy - but I have just done some testing and the results were as follows
I had Plex Media Server run as a Service with a plex account. The plex account was at this point an admin account, I changed the account type to be a normal user - non admin
I could still access paths within an admin account for which the plex account has no permissions
I then rebooted and tested running plex outside the service - I had no access to the areas the plex account did not have permissions
I then shutdown Plex Media Server and launched it as a service and that worked in same way - there was no access to the areas that the plex account had no permissions
See procmon capture
and Plex Web screen
It must mean that after changing the account type the service needed to be restarted
I do not know if your plex service account was an admin account before or not.
