That's too facile. Email was intended as a federated service that allows anyone to send mail to anyone. Privileging large companies over small companies and individual users is a clear violation of that principle, and a danger to the open and impartial internet. I get that spam is annoying (I hate it too) but letting giant American tech companies decide who is allowed to send email and who isn't is not the solution.
Imagine you live in an apartheid state and the people in power say: “White people will now refuse mail coming directly from black people. If black people want their mail to be received, they are required to send it through a trusted white liaison. If you're black and you don't like it, just make friends with other blacks and the tiny minority of whites who will accept mail from undesirables like you."
The above analogy is exaggerated of course, but I think there is a fundamental truth for it: large tech companies like Google have cornered the market by offering free solutions, and now they are imposing an apartheid system where mail sent through big companies is given priority over mail sent by real people who run their own email system.
(Personally, I've disabled all spam filters in Gmail since I've noticed that Gmail is likely to filter out legitimate email while the amount of spam I receive is actually very low.)