I’m not going to pretend that I know everything that Google have their tentacles in - because I don’t have that amount of time on my hands. And I agree with you that people should stop using their services.
If I misunderstood you, I’m sorry but… If I understand you correctly you propose that the only option to write emails would be with an email account owned by Google or one of their subsidiaries. To the best of my knowledge not every single email provider is owned by them - no matter how hard they try.
Notwithstanding the above, I too would be more at ease if support tickets could be handled by an internal direct messaging system within the itch.io ecosystem, rather that having to trust emails - a system that was meant as a temporary solution to begin with and should have been updated or replaced several decades ago. Such a direct messaging system would also allow users to have conversations in private. Just. saying… ;)
That said, I’m not blind to the fact that itch.io’s admins are currently hopelessly overworked, so I wouldn’t expect more than the admins taking our stances on the matter into consideration for future updates. (Or they could use Discourse, because that forum software is awesome…)