Something radically changed for me 7-10 days ago, wherein certain non-spam but clearly not-inbox-worthy emails are now consistently hitting the Inbox, often with the "Important according to Google magic" flag set.
Examples: A clearly promotional email from a manufacturer announcing new products, a special offer from a hotel I stayed at once 7 years ago, every single breaking news email from the Seattle Times.
FWIW, I'm not seeing proper spam by the old-school definition breaching the Inbox (Viagra, replica Rolex, et al). I guess that's good.
Still feels like something significant broke very recently, but tbh I'd already lost faith in Gmail's classification after seeing how many genuine emails end up in Spam the last 3-5 years. It's particularly painful to watch in light of how far other applications of ML have advanced since ole' Gmail was state-of-the-art. In other words: shouldn't Google (disclosure: my former employer) be much, much better at this?