Yes.
I could imagine in later seasons of TNG the command arrangement becoming more like in
Voyage to the Bottom of the Sea, with Admiral Picard in command of the missions, and Captain Riker in command of the
Enterprise, with Commander Data as second in command. After "The Best of Both Worlds", for example, would be a good time to promote Picard, Riker, Data, & others. And if Picard only gets promoted to rear admiral lower half instead of a higher rank, that would be due only to suspicion that he might perhaps still be partially susectible to Borg influence.
As for Sisko being promoted to rear admiral, at least, rear admiral seems like a very low rank for someone commanding such a large fleet.
I believe that in "Sacrifice of Angels" Sisko commanded a fleet of 600 ships in battle. Six hundred ships! If a group of 10 ships was commanded by a rear admiral, then a group of 100 ships should be commanded by a vice admiral, and a fleet of 1,000 ships by a full Admiral.
And in historical naval battles ships were often grouped in much smaller units than groups of 10. So if a group of, for example, 5 ships was commanded by a rear admiral, a group of 25 ships should be commanded by a vice admiral, and agroup of 125 should be commanded by a full admiral, and a group of 625 ships by a fleet admiral, and so on.
This article about the battle of Jutland in 1916 shows how many admirals were present in each fleet, despite the two fleets combined having less than half as many ships as the fleet in "Sacrfice of Angels".
https://en.wikipedia.org/wiki/Order_of_battle_at_Jutland
Suppose thate is a map of the galaxy on your computer screen which shows the entire galactic disc, which is about 100,000 light years in diameter, from above. Suppose that the United Federation of Planets is large enough to appear as an area on that galactic map instead of as a mere dot with no visible dimension.
Suppose that the Federation has a one star admiral in charge of the defense forces in every group of 10 star systems, a two star dmiral in charge of the defenses of every 100 star systems, and a three star admiral in charge of the defenses of every 1,000 stars systems.
If the Federation had two three star admirals under one four star admiral in charge of all system defense forces, the Federation would rule about 2,000 star systems. Surely that is a vast number of star systems and would make the Federation cover a significant area on galactic maps.
With the stellar density in the region near Earth, a spherical volume of space with a radius of 50 light years and a diameter of 100 light years would contain about 2,096 star systems. A sphere with a diameter of 100 lightyears would spread across one thousandeth of the diameter of the Milky Way Galaxy and would look very small and unimportant in a map of the galaxy.
Suppose that the Federation rules about 2,096,000 stars in a spherical volume about 1,000 light years in diamter.
If the Federation has a one star admiral in charge of the defense forces in every group of 10 star systems, a two star amiral in charge of the defenses of every 100 star systems, a three star admiral in charge of the defenses of every 1,000 stars systems, a four star admiral in charge of the defenses of every 10,000 star systems, a five star admiral in charge of the defenses of every 100,000 star systems, and a six star admiral in charge of the defenses of every 1,000,000 star systems, it would have two six star admirals under a seven star admiral in harge of all system defense forces in its 2,096,000 star systems.
Suppose that in the Federation, one star system out of every 10 to 100 had a highly advanced and industrialized Federation planet.
Thus a Federation 100 light years in diamater would have between 20 and 200 such planets. If each advanced and industrialized Federation planet could build between 10 and 100 major space ships for Starfleet each year, and provide a crew for them, the Federation could produce and crew between 200 and 20,000 major starfleet ships each year.
Thus a Federation 1,000 light years in diamater would have between 20,096 and 200,960 such planets. If each advanced and industrialized Federation planet could build between 10 and 100 major space ships for Starfleet each year, and provide a crew for them, the Federation could produce and crew between 200,960 and 20,096,000 major starfleet ships each year.
So any major space battle between major galactic powers, like the Federation and the Dominion were said to be, is likely to involve fleets of tens and hundreds of thousand of space battleships, and quite possibly millions of space battleships.
Suppose that in a major space battle, every 10 space battleships are commened by a one star admiral, and 10 such groups, 100 space battleships, are commanded by a two star admiral, 1,000 space battleships are commanded by a three star admiral, 10,000 space battleships are commanded by a four star admiral, 100,000 space battleships ae commanded by a five star admiral, and 1,000,000 space battleships are commanded by a six star admiral. That would involve each unit to have ten times as many ships as each unit immediatly below it, and therre are many historical examples of military and naval units containing a lot fewer than ten immediately subordinate units.
So it is quite possible for a space navy of a major galactic power to have far more than 6 levels of admirals to command of each 1,000,000 space battleships in their space fleet.
The rank structure of Starfleet, based on that of the USA and NATO, is totally inadequate in admiral ranks for a space opera space navy of an allegedly major galactic power.. Any major galactic power would have to have more levels of positions requiring admirals, and thus probably more admiral ranks, than all other officer ranks. So an officer who rises to the highest level in that space navy will spend most of his career in the admiral ranks.
And it is quite possible that in such a major galactic power, the space navy would have more ranks for admirals than all the other officer ranks, and all the warrant officer ranks, and all the enlisted ranks, combined. The US navy has 20 ranks below the admiral ranks, and I can imagine that possibly a major galactic power might be so vast it had more than 20 admiral ranks.
So I find it hard to believe that Sisko would command in a major strategic battle in the Dominion War as a mere rear admiral, let alone as a mere captain.
