My suggestion is simple and realistic. Those who practice the overwhelming firepower doctrine, would enjoy the same advantages as before, however, in the long term those huge ships will become a burden on the economy, and parking them in planetary hangars during peace time wont do. Refitting hull armor isn't that common task, but should be a considerable undertaking, and generally distinguish ships of different generations.
@alex_brunius .
You are confusing things. 2 ships will require more armor space, than one ship with all their content, all other maintenance related stats are either the same or infavor of the large ship. And there is absolutely no difference in cost of designing the same components. See this thread. http://aurora2.pentarch.org/index.php?topic=8244.msg85811
As for the rest I am not talking about a black and white scenario of only deathstars, but the simple concept that for those who have the capacity, building n ships of size X will be less efficient than building one large ships size nx. And with spoilers in mind, they have been around for millions of years, if there is no diminishing return to building larger, then you should encounter death stars from start.
I'm not sure if you have tried playing with actual large ships (400kt+) but I will take a guess that you haven't, vessels of substantial size require absolutely vast industries to even get them airborne let alone keep them flying. Take for example a 200kt ship at mid tech levels and you have the following issues.
1. You just bought yourself a 100k research project for the jump drive alone.
2. If you happen to have this thing armed with massive weapons there is another large amount of RP that are totally useless to anything smaller than this vessel. (in general with small ships you can reuse components on other designs with ease)
3. The amount of investment in shipyards you make means a double/triple/etc amount of minerals needed, time required for the tonnage growth, and population required to actually work there.
4. You need a much higher mining output to even have the materials to begin with, and to sustain the vessel for maintenance, this in turn needs a larger industrial output to build enough mining facilities, which again needs more population. In general this means having more colonies as you need a greater total population growth rate, which once again needs more of everything.
5. Once you finally get airborne you find your fuel needs are ridiculous and as such you have to really think about gas giants, this means either massive fleets of harvester or a few giant orbitals doing the harvesting. Either choice again is costing you industry, population and minerals.
5. You have to spend even more RP on things like shipyard operations otherwise it take eons to grow the shipyards to the needed tonnage, ship construction speeds if you want that monster vessel to launch in your grand childrens lifetime, and construction, mining, and fuel harvesting if you want to even dream about having the industrial capacity to actually pull off this sort of construction.
6. Finally if all that wasn't making your industry collapse under the weight you have the whole maintenance issue, either you now have a craft that chews up minerals anywhere it orbits or you have to try and construct giant hangers to house it. This really limits just where you can park the thing as it means hangers require massive amounts of construction also.
I'll throw a few numbers at you for example of this, in my current game I am currently only just able to start thinking about moving to the nest size stage of ships, this will mean I will be fielding 400kt command carriers and 200kt general warships with around 60kt patrol craft. I have had to devote earth to shipbuilding and industrial construction and nothing else. It currently have a population of 4bn and of that 300m are shipyard workers and another 500m construction workers. I know for a fact that when I do my ship size increases I am going to be somewhere around 200-300m short of population to actually work in those shipyards (around 4-6 years of population growth). To actually pay for all of this I had to look at really moving large amounts of minerals fast, I was quite lucky and 5 of the systems next to sol hold vast mineral amounts but at low access rates, this meant spending the last 3 years or so doing nothing but building some 7000 auto mines (since I did not have the population to actually use normal mines) and ship them out (which also required upscaling my freighters to get the cargo moved in that time period). I am about to also upgrade my harvesting operations to be able to actually fuel ships of this size which is going to mean switching to orbital habitats as the miners are likely to need to jump up to somewhere around the 300kt mark of just mining type parts. My current game I play with overhauls switched off but I do still use hangers just to keep my task group list somewhat tidy, now at this time with nothing bigger than 200kt I require a hanger PDC of some 5mt just to properly house a fleet which means some 55000BP to make so there are very few places I have the industrial output to build one, thus my fleets have to make long trips to and from the hanger which again is chewing up fuel.
So just to allow me to launch a proper 400kt ship (which is really not that large in anyway) I have had to devote my entire industrial and research output to increasing my capacity over a 7 year period. In that time I will have fallen behind in general tech advances compared to anyone sticking to sub 100kt ships. I have lost out on general expansion of the empire and as such have my populated colonies far less spread out than I would really like. You are correct in that there are only a small number of diminishing returns when going big with ships. But the overall knock on effect on your empire is vast, this is probably why we don't see NPR deathstars flying round. From a gameplay perspective building big ships is just total madness that leaves you wide open to conquest, the only reason to ever do it is for RP. There lies the biggest problem with trying to make it even harder to build big ships, this is not a multiplayer game and as such the player will always have the advantage of a human brain to call on for things like design ideas etc that will give them an advantage over the NPR. This then begs the question what purpose does making what is a very hard, long and frustrating process even more of all of those things actually achieve?