I think your definition of character is useful, and I tend to agree with Drucker that it's the most important thing, because otherwise a manager will subject to whatever political winds are blowing higher up without any grounding or point of view on what should be pushed back on. On the other hand though, "do[ing] the right thing regardless of negative consequences to oneself" is easily stated, but in practice is not effective without influence—if you are constantly saying no, you'll quickly be replaced.

The uncomfortable truth is that "the right thing" depends a lot on the point of view and narrative at hand. In large organizations political capital is inherently limited, even in very senior positions. It's especially challenging in large scale software development because ground-level expertise really is needed to determine "the right thing", but human communication inherently has limits. I would say most people, and especially most software engineers, have strong opinions about how things "should" be, but if they were put in charge they would quickly realize that when they describe that a hundred person org they would get a hundred different interpretations. It's hard to grok the difficulty of alignment of smart, independent thinkers at scale. When goals and roles are clear (like Apollo), that's easy mode for organizational politics. When you're building arbitrary software for humans each with their own needs and perspective, it's infinitely harder. That's what leads to saccharine corporate comms, tone deaf leaders, and the "moral mazes" Robert Jackall described 30+ years ago.

I think it boils down to knowing what your values are. If you're constantly saying "no" to your team or organization (or vice versa), then that's a sign of a values misalignment. At that point, your options are to push to change your environment's values, realize your values aren't actually what you think they are, or leave.

I agree that "the right thing" depends on point of view and narrative at hand (the context). And when I quote Drucker and point to character, I see it as the bedrock on which a good manager will stand. But people of good character still need a whole array of other tools to turn them into good managers: Being skillful politicians to navigate the organizational polity, being people who can see the big picture. Having _lots_ of people skills. Having a good grasp of the field of endeavor. An ability to laugh at themselves ...