That's fine really. You're not trying to hide the fact that you sent email from proton or anything. You're not using this key for anything else. It really does nothing more than provide E2EE for this email. So for compatibility you actually do rather want that to be published in the standard openpgp way so that it's compatible with other email clients and such.
I guess it would be nice if they gave me an opt out. This is just an alt to gmail though. No CIA shit.