I'm getting close to the end of my rewatch of DS9 and something keeps sticking in my mind every time I get to this point.
At this point in the war effort, Sisko leads many of the major encounters in the war.
Being the field fleet commander, it keeps sticking in my head: Why is he commanding the fleet from a Defiant class ship?
No contest here.
easily destroyed compared to bigger ships,
This one is false, you see just about every class of ship being torn apart without effort at one point or another in the Dominion war arc. The Defiant had ablative armor and took several shots to destroy.
usually lacks enough antennas / channels to properly maintain communication with the rest of the fleet,
This is speculation. There's no canonical evidence one way or another.
lacks personnel to help manage all the fleet operations and lacks science equipment to help properly diagnose the conflict to help in making tactical decisions.
There's a point here. But who's to say a few of the 50 people on board aren't CIC people?
The defiant is great for escort missions and short military survey missions. Afterall, that's what's designed for. But, its absolutely NOT a ship designed with the idea to command fleets.
If you want to get technical none of the Starfleet ships were designed to be fleet command vessels. The fleet was based on exploration. Ships can be modified for this purpose without much effort.
If Admiral Ross wants Sisko commanding the fleet, that's great for him, but shouldn't he have a ship to take into battle that's a little more up to the task of commanding the fleet?
Really the flaw here is having a Captain command a fleet. This is the equivlent of a colonel leading an army into battle. This was just a plot device to keep the main characters in the heat of things.
He should absolutely have a heavy cruiser assigned to DS9 for that purpose. A Nebula class would have been the minimum sized ship he should have been commanding
Nebula's are equivlent of Galaxy class ships. The ones with the weapon pod on top out gun them.
but one of the upgraded Excelsoirs, Ambassadors or Galaxy class ships is what he really should have been riding into battle with if he was the fleets C&C, or at the very least a wing commander.
Really though, Starfleet's not going to assign a heavy ship like you mentioned to DS9 as a sentry ship. If Sisko gets command of one of those his days at DS9 are done.
It would have made more sense for the Defiant to always remain close to the station. Heck, it would have made more sense to see the Defiant more actively orbiting the station along with that Yeager class we usually see rather then constantly docked when it wasn't on mission. I mean lets face it, DS9 only ever seemed to have one other (including the Defiant) support vessel from Star Fleet on patrol around DS9. I can certainly forgive not having heavy cruisers there, but it always felt like there should have been 3-5 Akira, Norway or Streamrunner type ships there at all times.
Akira's are classified as heavy cruisers technically, even if they're on the small side of the spectrum. Fact of it is, unless they are there to be picking up supplies or getting repaired, they're at war. They're gonna be at the lines. If Sisko is captain of a ship with as many crew as his station, he's gonna lose command of the station.
Heck taking that a step further, it would have made more sense with Sisko ridding one of those in fleet command situations over a Defiant class (not that that really would have made a lot of sense EITHER).
A Norway or Sabre would have been a nice replacement to the original Defiant for variety in my opinion, but again if Sisko gets command of a large ship, they're giving the station to someone else.
