According to RC's own knowledge base, this feature did exist at one time: https://support.ringcentral.com/article/10644-user-roles-permissions-set-default-role.html
Backstory: we decided not to utilize SMS messaging in our environment. So a custom role was created that is exactly like the Standard (International) role but with SMS features turned off. This new role is what all our standard users should have.
Our Level 1 techs are assigned the User Admin role and are responsible for onboarding new users. The only way currently to allow them to assign the correct role at account creation is to give them the ability to change roles for all accounts. This is a huge security no-no from an administration perspective. If you were to restore the ability for a Super Admin to change the system setting for the default role of a new user, then every new user would be set up correctly and any changes would be escalated to the Super Admins for review.