Well, there are alternatives. There's /e/ (murena.io now a days) and distroot, and you can use gnupg with others who also use gnupg, and with distroot you can use its own encryption as well. There's tutanota and prrotonmail, which use their own encryption mechanisms but only work with the same providers and not with other providers...

I mean there are already several non big corps providers of email. Distroot also provides xmpp, nextcloud, and several other services, the same as /e/. I can't tell I'd trust more TB than the alternatives, several of them are non profit. But there are options. It's sad before smart phones, some big corps were already dominating the services, and after them, things got even worse. But there have been, and still are, options for refugees. That's not the issue in my mind.

The big issue, is that those big corps do what they want, excluding those not using them. All of them, no exception, place received messages from /e/ to the spam, that if the email even reaches the final user, some times it gets discarded by the service without even getting to the end receiver. Several mail registrations for whatever account, banks, insurance, stores and so on, don't even accept email addresses if not from the big corps. So the huge and toxic influence from big corps doesn't get corrected by another non big corp service. It's like with FLOSS alternatives, or more private alternatives in general, the issue is the power most users give to those big corps. Most users prefer those corps services, at times ignoring the non big corps are not less comfortable, but most of the time they don't even care, even if told there are easy enough alternative they would still select big corps. Then with such power, big corps not only dominate, but also discriminate non big corps users...