Personally I see this as just more Google incompetence. Gmail has just become bad. If you want to get all your mail you have to use something else.
It's like we're going back to the days when each e-mail service only trusted messages from its own users, and if you wanted messages to go to another network, you had to use an e-mail gateway.
I don't think this is a general problem with e-mail services. If you use an e-mail provider that's a paid service rather than a pipeline into an ad company, you actually get good service and a customer support team that has an incentive to fix your problems. (I've been very happy with Fastmail for many years.)
