A officer who has declared their intent to separate or not seek DH/command is not best suited for command. Wouldn't you agree?
I wouldn't. Reason being is it's up to the CO to say who he thinks is best. The point of being a CO is that you have the wisdom and experience to see things that the folks working for you may not or cannot (due to lack of experience, less SA on the big picture, etc).
Just because someone says they are getting out, and even says they don't want CO, doesn't mean they wouldn't be the best choice.
I'll use a different example, the Level IV designation. I was made a level IV in my first fleet squadron as a LT, while on deployment, and I still had about a year left in my squadron. So there I was, a LT, a little over two years out of the RAG, and I'm SWTP Sea Combat/Strike level IV, flying and leading in 5th fleet.
My point with that example is that I personally didn't think I deserved level IV and I wouldn't have asked for it, but my CO, who had a helluva lot more experience than I did, knew that I was ready for that.
The same thing applies to the FITREP and best ranking. The CO makes the decision who is the absolute best and should rank accordingly. That may mean that the absolute best doesn't stay in the Navy, but again, that's not the CO's problem, that's the Navy's problem.