I still think that lonely large battleships gonna be nothing more than bulletsponges, ever asked yourself, why in WW2 Bombers flew in formation with fighter escorts (Edit: They still got torn to shreds even while flying in formation and even with fighter escort)? Thats right alone they got torn to shreds, and i believe nothing else will be the case in Starbase. It's not that I dont wanna see these type of ships, its more of: They can exist, but they are basically worthless in anything but a supportive role like carriers. Another example of this: The core of the modern sea warfare are Carriers. Why? Because as good as you can protect yourself, there is probably going to be a fighter who can kill your entire ship with basically one missile
While I don't think large ships will be very effective in large scale combat encounters, I do believe it would be possible to create a mobile base of sorts for patrolling the belt.
But on combat, a sufficiently sized crew can man multiple gun turrets in case of emergency, and since larger ships can boast heavier plating, especially now with the new plasma thrusters, it really comes down to if the aim of the gunners is sufficient enough to snipe the meta heavy fighters they are up against. The only real threats I can see large, mobile base-type ships facing are stealth fighters equipped with maneuver thrusters only, designed to snipe with railguns, similar to some ships currently seen in the alpha.
Back onto my main point, mobile base ships could be a viable option, especially with how dense and large the belt is now. If it becomes possible to manufacture all the resources required to run ships, such as propellant and fuel rods, onboard a moving ship, it will open up the playstyle of the belt scavenger, cruising around the outer rim in order to maintain long flight.
If ships like this remain exclusively in the outer rim of the belt, they could sustain themselves without meeting much force, as fighter squadrons would be incapable of spending large amounts of time searching for a deep miner. Unless of course, they make a similar ship of their own into a carrier-type ship to haul their fighters around, which of course means this type of ship will have an even larger presence in the meta of the game.
To cap off, I do not think large battleships will be very useful for large-scale conflict, but for a more roaming playstyle, or as a carrier for fighter squadrons, they could become pivotal in the dynamics of the game.