Yep. I agree with Abi. I also I think this is true in any industry. Or even just as a taxpaying citizen. It’s just really hard to have one’s ethics be completely aligned with anything. But exiting doesn’t make those ethical problems disappear. You just leave them for someone else to deal with.

Good questions. A few thoughts:

1. I think your assumptions are generally right, but I'd add one: One's authority in a policy space is somewhat proportional to the number of other people claiming expertise. The junior staffer who's been laboring on an otherwise ignored issue will skyrocket in value at the moment of crisis. For example, how many Ukraine experts were there last year compared with today? If that junior staffer can rise to the moment, they can launch their career on a new upward trajectory. Meanwhile, comparably few officials are working on the war in Yemen right now, which the UN has described as the "world's worst humanitarian crisis."
2. US Diplomats spend an average of a third of their career in DC and two-thirds abroad. In this manner, the foreign service offers you multiple perspectives. You'll understand issues not only through the DC-centric lens, but also Beijing, Brussels, and Buenos Aires. The power lies in DC, but it's harder to build real expertise and relationships sitting behind a computer screen in DC.
3. Building on the above answer, I'd ask: What's your network for? Building expertise and influence are sadly not always the same thing. If you want to build expertise on an international issue, it may be a significant advantage to build a great international network on that issue. That's not something you can build easily from home. Living/working in DC is a significant advantage for building influence in DC, but that game is much easier if you also have recognized expertise. The foreign service isn't the only way to build up expertise and influence, but it's a great one, and it's more accessible the most other pathways. But hey, if someone offers you a job on the NSC, go ahead and take it!