And this is happening after SPF, DKIM and DMARC provided a solution to the spam problem.

Any mail system can remove practically all spam by insisting messages conform to those three standards

But that is not true at all. Spammers can easily send mail with all proper SPF, DKIM and DMARC records and signatures. A lot of spam is and will be sent like that. Those extensions do not make spam impossible, they just make it easier to track and block.

But this does not change the point of the article – in this case it is a specific domain sending very specific non-spam messages. SPF/DKIM/DMARC prove it is not someone else – GMail has no ground for blocking these (unless were are not told something).

And GMail has been breaking mail for years now. E.g. I hate them for breaking message threading by ignoring threading headers and forcing own view on how messages should be grouped.