My bad, I forgot 3 or 4 = 500 and that 2 = 79001024093789327382974328943^(32388383999). Tell me, why exactly is 500 (read 3 or 4) impossible for an 800 to 1000 meter long warship? Do we have canonical size restrictions, canonical beam power usage, and canonical power plant output?
It's a hyperbole.
I think it goes by common sense. If no Terran ships of a certain size have 4 BGreens, it stands to reason that the reason there isn't one is because it's not bloody possible.
Not true. It's possible for aircraft carriers to mount 14 inch guns that shoot nuclear shells, but none of them do. Why? Because they're effective without them. Are fighters incapable of using flak guns? By your logic yes, but in this case, you'd be a bit suspicious. The size and damage of flak shouldn't be too big you mount on a fighter, though you wouldn't be able to load too many shells. Is an Orion capable of mounting Morning Stars to fend away bombers? By your logic, it isn't. Think up a more logically sound argument other than "it doesn't balance, and it hasn't already been done".
It's not a common sense thing that this is impossible. If you want to have a balanced game, then it is. If you're actually going to use this concept to make a ship for the game, then by all means, disregard my idea. But if you're honestly trying to think up an extension to the GTVA fleet, with a relatively realistic military design strategy, then shouting "YOU CAN'T HAVE 3/4 BGREENS ON A CORVETTE BECAUSE IT WOULD WORK TOO WELL" has no place here.
A hunter-killer craft that I described is a highly specialized warship. As I said before, it wouldn't be used for normal combat. If they were, they'd be slaughtered by any wing of bombers that looked at it wrong.
A Deimos or Sobek is not a specialized craft. They're meant to be used against fighters, cruisers, other corvettes, and many other numbers of things. And they're effective at that. The things that they're not effective at is quickly dealing with them.
The hunter-killer that I described wouldn't be a cheap ship, as evident by the 4 Bgreens. There wouldn't be many of them, mainly because of the expense and that not too many are needed. More than likely, they'd be used by SOC. But it's effective at the one thing that not too many other crafts are: Quick, highly lethal, and relatively uncounterable attacks.
Why not use this tactic on all of our ships, then if it can decapitate a fleet so quickly? Because it's expensive and ineffective against certain tactics. For a populated area as large as the GTVA, you need a fleet of a certain size to be able to defend it and maintain order. With ships this expensive, you wouldn't be able to do that. But let's say for a moment that you magically do manage to get enough to do that, through some evil manipulation of FRED. The enemy counters that move with similar ship types of it's own, except with a higher dedication to electronic warfare and early detection and bomber ability. Now the enemy has a fleet of cruiser/corvette hybrids that have double your ship's sensor range, a squadron of interceptors, a squadron of bombers, and no guns, all for half the cost. Now it's them mounting the raids on your ships, because our hunter-killer fleet is incapable of defending itself from such amounts of fighters and bombers. Now let's say that your ships can effectively do everything really well, and you magically can afford everything to have a satisfactory fleet size. Hurrah for you! You have a highly effective space-borne navy. Give your R&D team a cookie.
But that doesn't happen because we're assuming the GTVA will be in a near economic-paralysis after the SGW. So they won't be able to afford any of these ships for a long time, because they need to rebuild their economy and regular fleet first. Eventually they would be able to afford it; I'd give it 10 or 15 years, seeing as how quickly they managed to do things after a 14 year-long war against each other and then against the Shivans.
EDIT: BTW: If we all defined rules beforehand that govern things like power output, weapon size, and logistics, would anyone be interested in creating a fleet for the GTVA for 30+ years after the SGW? I figure we make a thread to define the rules and once that's done, we make a thread to actually start. If people are interested, then I'll write a template to begin discussing the rules.