I actually find frigates to be the most useful precapital ship in 1.04 Partially because I most often play on large or larger maps where distances require greater speed, frigates are pretty darn fast, pack a whollop, and have stats high enough to be influenced by Military Starbases. If you have access to a military starbase, it really magnifies the advantage of the bigger ships over the smaller.
In the game I'm playing now, I conquered two AI completely (about 30 stars total) using a force of frigates and transports, with a few axes for defense. One AI was wiped out and the second was down to its last planet before I built my first battle ship.
The extra delay to get to the capital ships actually make it kind of fun to play around with the lesser ships, rather than just rush to dreadnought.
A defender at a planet with the planet bonus can ward off surprise invasions and fares pretty well against ships smaller than a frigate.
Fighters are very useful, because they are fast and can intercept enemy transports and constructors at a distance. Since the AI rarely ever stacks ships with transports you can infiltrate their fleet and snipe their transports using fighters, and when their warships counter attack...so what fighters are cheap.
Scouts I actually find usefull in the early game as combat vessels. In the late game with dreadnoughts which can do everything well, recon isn't very important. But in the early game the ability to put a good defensive ship where its needed and to detect where the vulnerable enemy ships are to send your attack ships after without wasting movement is pretty important. I try to infiltrate scouts into an enemy fleet as my first move...then I can count squares to determine the ETA till a planet gets invaded or launch attacks to maximize damage. Scouts also make great bait. For whatever reason the AI prioritizes them as a target. I've saved a planet from invasion, by delaying the enemy warships by feeding them scouts which they were willing to reverse course in order to kill.
Corvettes I don't generally build because its a dead end tech path. Shields and phasars and the like have usefullness beyond the ship they produce, but corvette tech doesn't. I'd be tempted to make corvettes a prereq for frigates, but that probably limits the options too mucb.
Battle cruisers are ok, but I never use them unless I get stuck in a war in exactly that point where I need a ship now and frigates are too far away. Otherwise I skip them and go for the frigates. BCs are actually I think the great weakness of the AI. The AI builds FAR too many of these, and then counts them towards its own military ability. Not only does the shear number of them drain the economy (which on the tough levels doesn't matter because they're swimming in money anyway), but it gives the AI a false sense of security. They THINK they have a powerful military but if its mostly BCs its alot more fragile than the numbers suggest.
I don't know what the military formula is, but there should be 2 formulas.
1 for evaluating how secure you are and able to blow off enemy threats.
This formula should be (2xdefense + Attack)* Hitpoints * 1/2 Speed...per ship and then totaled.
The other should be for evaluating how able to project your power on to others you are and kick their ass aggressively.
This formula should be (2xAttack + Defense) * Hitpoints * 1/2 Speed...per ship and totaled.
Additionally, the repair rate should be factored in to the attack formula especially, because it determines how long you can keep pounding away with your main fleet before you have to stop and repair.
I also think that the formula should be calculated seperately for each sector and then the sectors organized into districts. The districts would be named after the enemy players. The anti Drengin district, the anti Yor district etc. A sector would be included in the calculation for a district if it is within 2 sectors (on a large map, scaled accordingly for others) of that enemies star systems.
This would allow the AI to act a little bit more intelligently on who it declares war on and who it pays tribute to. For instance, if the AI has a high military score, it might try to intimidate me into paying tribute. I refuse. The AI declares war...but the majority of its fleet is clear on the other side of the map a year+ away dealing with the Torians. By measuring specifically how much of its offensive capability is just in the sectors within striking distance of me, the AI would be better able to evaluate if its ready to declare war or not.
Similiarly if the Drengin challenged for tribute, the AI might be more willing to pay if the Anti Drengin District score was low, even if over all the strength was high (or vice versa).
Just a way to give the AI some more info to make decisions with.