I did some tiny digging because I remembered that there is a way to report individual messages in a structured machine readable way to abuse@ for these things --- i suspect that this is technically supported by gmail (if not given a lot of signal weight)
https://en.wikipedia.org/wiki/Abuse_Reporting_Format
How to bulk do this is interesting too. https://en.wikipedia.org/wiki/Feedback_loop_(email) says that gmail has a bulk format and that sendgrid is seeing some success.
Not defending just trying to see what a technical solution looks like