The in lore reason the SLDF didn't care is that they could field more Battleships than any of the individual House Navies had in total warships. You might win a fight here and there, but there's always going to be another SLDF task force coming your way, there's always going to be another battleship or two, there's always going to be another SLDF mech Division to land on your planets. I'm not saying you couldn't make a game for it, or that it wouldn't be fun as hell, but you're better off from Clan Invasion on if you want warship fights. The Jihad had more than a few. But dropship scale is where it's at and it makes me sad that Catalyst hasn't made more pocket warships. Warships are slow, lumbering bricks of capital-scale guns and armor that can annihilate anything smaller than them in short order. Using an 8/12 thrust Achilles to out turn and burn fighters? That would be fun.
Yeah, it doesn't have to be about Star League era WarShips, I'd be absolutely happy with jump-incapable Pocket WarShips duking it out during the late Succession Wars or in the time leading up to the Jihad.
But, then again... A game that covers the Amaris Civil War era and those epic space battles would be pretty fucking swell, too. Start out with the coup and a desperate attempt to fall back, regroup and escape, a long drawn out campaign against the Periphery, the subjugation of the Rim World's Republic and then the final push towards Terra.
You could go for a sequel that covers the first and second Succession Wars, when WarShips become extinct.
The game could show off how the fighting goes from autistic slapfight between wannabe-First Starlords to full out scorched earth genocidal warfare, culminating in the eighth Battle of Hesperus II, where all remaining WarShips are ground to irradiated spacedust.
I kinda envision a twist-ending where the player character and his crew survive on a barely functioning WarShip and after witnessing the effects of the Succession Wars they decide to join ComStar and become part of their shadow fleet.
It would be a pretty unique opportunity to give the players first hand experience of a time period that we usually just see mentioned in passing in these games from a completely new perspective.
You'd just miss some of the more fun Aerotech rules, like High Speed Passes. What does happen when you hit an enemy ship with a kinetic weapon after accelerating in-system at 1g for a week? It's not pleasant, but you only get one volley.
Kinda reminds me of the novel Flashpoint, where the Avalon class ship "Robert Davion" gets destroyed in a somewhat similar fashion after being rammed by a barely functional dropship, flung at it by an Octopus-class salvage vessel.
On a sidenote: Do spacebattles use the same ranges as ground combat?
I always thought that jetfighters and spacefighters in BT are a bit wonky due to their short weapons ranges. I wouldn't mind special case rules that double (or even tripple) ranges for air-to-air, ground-to-air and air-to-ground combat (based on LOS being far less obstructed than it is for ground vehicles fighting one another or some similar explanation). In a similar way, increasing ranges for space-combat by an order of magnitude would be acceptable to me, assuming the ranges aren't already longer than for Mechs...