Ahh “open rates”. The great lie of the email marketing industry. Those numbers that Marketo and company show are either completely made up or at least have hidden “scaling algorithms” applied.

All modern email clients block all image and CSS requests by default, and email security filters examine any linked URLs automatically. So there is no reliable “opened but did not click” feedback mechanism at all in modern email.

Set up a seed list of 100 email addresses you control, send through email marketing tool of choice. Open exactly 1 of those emails from a default client. See what lies their “open rate” dashboard gives you.

As was clear in context: Google evaluates the real thing for inboxing. It is relevant to which tab your emails get placed under. Hence all the advice to remove people who don't engage.

Whatever open rate stats are shown to marketers are irrelevant to google's deliverability choices.