This ship is classified as a dreadnought. By definition, this ship is a combat vessel with heavy caliber weapons. It is not a transport vessel.
Our current Navy is working on building drone ships that will monitor submarines. Though they have things common to all ships, they are designed differently.
This is an example of an anti-submarine vessel.
Now, applying this to Federation starships. This Dreadnought Class starship is essentially a combat drone with limited crew interface, probably for controlling the vessel manually from a bridge. They may need a few decks for a sickbay, quarters, and mess halls. The rest of the ship would be occupied by equipment for the weapons and the engineering.
What do I know about Federation starships? They are composed of two major hull structures: a primary hull which houses and sustains the crew and a secondary hull which houses main engineering. In some classes, these two hulls are condensed into a single form.
So, when designing this new ship, why wasn't the two hulls condensed, so that there would be one hull which housed the main gun? I have seen fictional ships designed like this. In Mass Effect, there are dreadnought type ships which have a single hull housing a massive mass acceleration gun. The gun, or what I have seen of it, for this new ship looks less like a phaser, and more like a mass acceleration cannon. (I am not saying that it is a mac; it might be a fancy phaser cannon that requires rails for the launching of the "shell".)