I imagine this is where the reputation of a good manager comes in and the ability to say to their boss "hey, we should keep this guy... just trust me on this."

Good managers are fairly rare, even though every manager probably thinks they are a good manager.

I'm one of the few who absolutely believe they're not one of the rare "good" - hopefully, "not yet".

What resources do you recommend to improve ?

I think thats a good start probably haha. I am not a manager, and have not had a "good" one in a very long time, so I have no resources unfortunately. That isn't to say mine are bad, they let me be autonomous as an IC and I have a lot of flexibility. I am coming more from a human angle, and not a "these are the 5 things you need to do to be a good manager" angle. In my company, most people are too busy with day to day activities to really focus on developing people. When I parted with my last one, he thought we had only been together for 2 years...it had been 5. I think a lot of managers just don't really listen, they nod their head and give some advice and then 4 weeks later we're just having the same conversation again.

Everyone's situation is different, so without context this probably just reads as pouting or possibly me being incompetent haha.

radical candor is a good book that explores a simple framework for people management.

A massively abused book that led many to justify being assholes. You don’t have to read it, here’s the Cliff’s Notes:

Care personally, challenge directly.

If the company runs on reputation it’s only a matter of time until a consultant comes in and processes are established to move to a more efficient metric based management style.

Yeah, it's tough either way. Some managers might be biased and keep praising some of their reports that don't actually provide good value for the company. For an outside observer that has no intimate knowledge to the work, how could this be differentiated from the manager having a backbone to support a report that does truly great work but there is no good metric to prove it?

Depends on leadership culture. In toxic (aka “competitive”) environments managers are insecure and fear their own staff as potential competition.