The reason why no research is needed for cap ships is because the dev's want them built early so they can fully level up by the end game. To a point i dont agree with that. You can still research a ship, build it, and still have it in your fleets in plenty of time to fight enough battles to level them up. Plus by researching some cap ships it will make the smaller ships even more important, because you will have to rely on them longer. Not all of the caps need to be researched IMO. Heres what i think.
The Kol, Marza, and Sova should be researched. The Akken (spelling), and Dunov i dont see an issue using right away since they seem to be the converted civilian ships. They dont have much firepower, but where they shine is in their abilitys.
The Kol. You get one in the beginning of the game as your flagship if you chose flagships. Consider it a Prototype, and a gift. So you better protect it! Since according to the lore it is the newest TEC ship design. Plus being the most powerful cap ship TEC has it MUST be researched to be able to build more of them. It should be high in the tech tree to reflect this (lvl 5 or 6 maybe, and very expensive to research).
The Marza doesnt look, or act like a converted freighter. It looks, and acts like a new TEC design built around a BFG

So researching this is a must as well. While an older design than the Kol it is still quite powerful, but i wouldnt use it as the sole cap ship in a fleet. It lacks the firepower needed for a stand up fight, and it is very vulnerable to bomber attacks. The ship is designed to be a support, and planetary siege platform. I say put it around mid range on the tech tree, and a moderate cost to research.
The Sova is similar to the Marza in that it looks like a newer TEC design vs an old converted ship. Plus it can field a ton of bombers when fully leveled up. I say research this one as well, but put it low on the tech tree. Around the same area the light carrier needs to be researched, and at a reasonably low cost, because im sure carriers are nothing really new to TEC. Just this particular ship design is new.
The other 2 cap ships fit right in with the lore, and are similar to the newer cruisers in that they dont have much firepower, but can support a large force of frigates. Which is what they were designed to do. Being converted civilian ships no research should be necessary to build them.
Thats just my thoughts on the issue.