Yes, that's true, but as I am constantly reminded by others, Starfleet is not the modern US Navy.
Agreed, it's just a little hard to for me to believe a major vessel like that would be commanded by a junior officer, or, with a rank structure so similar to those of the r/w, that commanding a Starship is a lower-grade post than a nuclear sub today. Also, Pike introduces himself as "Captain Christopher Pike" to the
Columbia survivors in "The Cage," when you might expect to give his official rank, and "Captain Christopher Pike" is noted as the commanding officer of
Enterprise in official proceeding in "The Menagerie." It's just easier for me to swallow that the stripes on the pilot ep uniforms do not mean the same as they do later.
Besides, if we're actively trying to retcon Spock's rank, Kirk's rank, and Pike's rank based on sleeve stripes, I don't think TNG/VOY/DS9/ENT have much to teach us.
Or the rest of TOS and TOS movies? It's just that it appears Starfleet policy is decidedly on the side of having its vessels commanded by senior-grade officers, and has been for some time.
--Justin