I'm not defending gmail, but I will say that some users simply suck (unintentionally). I bet some of your peers are just hitting the spam button instead of simply deleting the email, generating a bad reputation for the sender.

I've seen this with my SaaS. We ONLY send transactional emails like purchase receipts and login links (using postmark). We're very intentional about not sending anything remotely resembling marketing or spam, and sending as little as possible. Yet I still get the occasional user who will flag their purchase receipt as spam when all they really mean to do is delete it. They don't get the difference and don't realize that it matters which button they click.

I've noticed that in the past year or so gmail has made hitting the spam button more explicit and now have a confirmation message. Obviously they did this because some people were simply mashing that spam button instead of the delete or archive button.

I don't even blame the users. Most don't know the impact it has. But bad actors sending tons of spam have trained them to be cynical of any generic form email.