That didn't work for me.

My domain is still set up with G Suite with SPF and all so Google is technically fully capable of sending emails on my domain’s behalf, but if I got the "me@example.com via example@gmail.com" text regardless.

My setup:

    1. log into example@gmail.com
    2. set up "Send as me@example.com" with alias
    3. enter example@gmail.com as the SMTP username

Headers:

    ARC-Authentication-Results: i=1; mx.google.com;
       spf=pass (google.com: domain of example@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=example@gmail.com
    Return-Path: <example@gmail.com>
    From: Me <me@example.com>