How to use Gsuite Relay as SMTP for CiviCRM bulk mailing?
It seems there is a difference between sending via Gsuite and Gsuite SMTP Relay ... 

For sending via Gsuite, and comparing the connection details in the post you linked to with a site using this, the difference is that it uses SMTP host ssl://smtp.gmail.com

The main practical limitations are the limits and that all mails get sent out with the sender of the Gsuite account, not the address you configure in Civi.

I haven't tried Gsuite SMTP Relay