in install process, choosing url access mode, you can set a user path in the same step you choose the database.

i would expect this path should the "default" one but is not.
btw, your admin path is respected.

user path is added to the sitelist array and to the availablesiteaccessList, but is not the default one

Steps to reproduce

do a fresh install
choose www as your user path
choose administration as your admin path

check your settings/override/site.ini.append.php and you will notice your selected user path is not the defaultaccess