this is the pragmatic take that matters. i've dealt with this exact dynamic with app store review processes: the guidelines say one thing, the reviewer interprets it differently, and at the end of the day you just fix whatever they flag because shipping matters more than being technically right.

the email situation is the same pattern at scale. google workspace has the market power to enforce whatever interpretation they want, and the RFC debate is basically irrelevant from a business perspective. your users don't care that your reading of the spec is correct, they care that they didn't get the receipt.

the part about a payment processor not testing deliverability is wild though. that should be in the first week of any transactional email setup: send test emails to gmail, outlook, yahoo, protonmail, check headers, verify SPF/DKIM/DMARC, and actually monitor bounce rates. the fact that a major processor missed something this basic suggests the email infra was probably a "set it and forget it" setup from years ago that nobody ever revisited.