I disagree, it’s the tying of your email address to a provider. If your email goes to “first@lastname.com”, then a quick MX change side steps a Google ban trivially.
But if your email address is “name@provider.com”, you’re kind of screwed.
Now the problem is making the acquisition, setup and maintenance of personal domain names and mapping to an email account something the average literate adult can manage.
…and chuckling ruefully as I recall walking recent college grads who are far better devs than I am through what needed to happen for SendGrid to actually work for one of their project, having to start with “what is an MX record?” and “where is that controlled?”
But if your email address is “name@provider.com”, you’re kind of screwed.