The idea that you can trust a company of that size, even if they didn't have the ambition to grow tenfold in five years, is completely antithetical to any sort of goal of 'data sovereignty', or Big Tech independence.

Any company with a hundred million users is too big to fail, in terms of accountability. Heck, I would argue that even a million users is already too much for a healthy internet, and especially for email. That kind of volume should not be concentrated with a single commercial entity, no matter how much you like the stories they tell about privacy, being owned by a non-profit foundation, and so forth.

The dynamics just change, and do so well before you hit that number. You start thinking in percentages, instead of about individual people, and that is not really something you recover from.