Mostly covered elsewhere in this page, but in my opinion, gold PMs understand, on a deep level, the intersection between user needs, the marketplace, company strategy, and the engineering resources available; don't take shit from any of them, and can balance each of them.
1. User needs: this means not just talking to users, but seeing how users use your product and competing products. You understand what users are actually trying to do. Not taking shit from users means, just because a user tells you they wish something existed, therefore it gets written down as a feature request. Maybe something else would be better, maybe the user is a sourpuss who is giving you crap because they're having a bad day. Gold PMs read the room. Allowing every user direct write access to the feature request lists is design-by-committee and guaranteed to result in crap. Gold PMs know how to filter out everything but the most essential.
2. Marketplace: Gold PMs understand what other products are in the market. They understand that the market chooses between different products in the market, and therefore, what's important is how to differentiate the product within the market. Good PMs understand the difference between a feature that other products have that needs to be built in their product (i.e. table-stakes/non-negotiable, like SSO in Enterprise products), and not taking shit by adding features just because other products have them already (the building of which won't help differentiate their product in the market).
3. Company strategy: Gold PMs listen to executives who say which market segments the company is trying to reach so that they can reach out to the relevant users and choose relevant features, and not run after irrelevant segments that don't fit into the strategy. Not taking shit means knowing when to push back when executives pick a market segment that isn't going to be interested in the product (happens more often than you'd think), and making sure that the team has the budget and resources to go after (i.e. talk to users in) that market segment.
4. Engineering resources: Gold PMs understand, roughly, the skills of the engineers and developers who are available to them to build the features. They know what feature requests are feasible, approximately how much time it takes to build them, and when they need to back off and let engineers pay down technical debt. Not taking shit from engineering includes concerns like: not allowing Engineering to build feature work that they feel is really important but hasn't been through the Product process (market research, UX, etc.), pushing back when Engineering says something will take much longer than you think (i.e. is it a misunderstanding over scope?), pushing back when Engineering releases half-assed work (i.e. almost like QA in terms of exploring edge cases in the Product, and making sure those are addressed).
Gold PMs are valuable to Engineering when they distill user needs + marketplace + company strategy into a very simple list of the top 3 things that need to built in the next two weeks, and can clearly explain (including showing their work) why those 3 things are at the top. They are anchors when those top 3 things are clearly bullshit, when they don't even bring you a list of prioritized features to build, when their presence is required to get anything (even non-feature work) done, when they push paper for the sake of pushing paper, when they get in-between you and necessary externally-sourced information (design files, customer feedback, bug reports, etc.).