This is one of the issues that hopefully (!) the second season edition of "These Are The Voyages" tackles.
A few thoughts:
1. Decker seems to be the captain of the Constellation
, certainly. He records a "captain's log" and calls himself the captain when he explains to Kirk why he's the only member of the crew left aboard:
"Oh, I had to beam them down. We were dead. No power, our phasers useless. I stayed behind, (the) last man.... captain, 'last man aboard the ship.' That's what you're supposed to do, isn't it? And then it hit again and the transporter went out. There they were.... down there, and I'm, I'm up here."
2. I suppose there are certain starship captains--fleet captains, maybe--that had overall command of a particular sector, or group of ships (though, not necessarily other starships). Decker would qualify for that.
3. Wesley is a whole other matter than Decker. First, we have to revisit some old ground for my point to make sense.
We know (or can smartly infer) from other threads that Decker's uniform got a new patch that was meant, I believe, to signify that he was a member of the Constellation
crew. I suppose it could mean that he's a fleet captain equivalent, but the fact that Capt. Tracey got his own unique Exeter
ship patch when we know he was a 'Kirk equivalent' leads me to believe the former argument holds.
So if Wesley is the captain of the Lexington
, why... oh why does he wear a Starfleet Command patch? Shouldn't he have a separate patch along with the rest of the Lexington
crew? Or if Decker's patch meant he's a fleet captain, why doesn't Wesley wear the same patch?
I think Wesley was a member of Starfleet Command and a former starship commander--perhaps even as a commodore--and for some reason he replaced the Lexington's
captain for the M-5 test mission.