I self-host on a VPS, so my off-site copy is the VPS, and my on-site copy is the emails downloaded to my email clients.

I figure that Proton or Tuta are probably still safer than Google.

Define "safer". If you are receiving unencrypted emails (which is the case in the vast majority of cases), there is nothing stopping Proton or Tuta from reading them. Fundamentally, if something arrives at a server unencrypted, the server can read it—nothing can be done about that.

If you're exchanging e2ee emails, then it doesn't matter if you use Google, because the body of the email can't be read by Google. A lot of metadata is required to be unencrypted though (this is the case for Proton and Tuta too).

I don't really see the benefit to using an email service like Proton or Tuta from a perspective of meaningful data privacy. If it were between e.g. Proton and Google I'd probably pick Proton to avoid my emails being used to serve me ads from Google, but I wouldn't have any illusions about Proton being able to read unencrypted incoming mail.