if you make fleet support dependent on capital ship support
This level of control is not available to the modders.
if you set the resource requirement for the ability higher than the cost for a normal capital, the AI will still have the option to build a normal capital.
The AI does not make the decision. It's a random process based on AI saving trends and available fleet/capital slots.
Even in my test game they had build their first normal capital before they got swamped with dreads
Yes the AI builds its first capital early.
Of course the question is how the AI will react to having some dreads, maybe they stop building capitals of that class, but this could be countered by giving other capitals a different class.
Your considering change the TEC, Advent and Varsari capital ship lineup ... don't wont to change the original races, they have been optimized by the original developers.
Limitation of the dreads is speed and agility. They tend to collide with other ships and if you have more then one it becomes ugly. I think you should extend their default weapons range to avoid the mess in battle. Then you could also move them back in formation e.g. by giving them carrier class. This would further reduce the formation mess and at the moment other ships are overtaking the dreads who at the destination then push through the other ships to come to the front. The current carriers could become a support class, so the AI would still build them eventually.
Good points. The Dreadnoughts were meant to be the equivalent of a starbase for original Sins (similar to starbases in E & D), hence the size of the models.
What just comes to my mind: alternatively another ability could be added to the ship yard to spawn normal capital ships. This way you would take "control" of ship building, but the capital ship support limit would be useless then.
Unless you make the abilities kick-in mid to late game.
I'm still not seeing a clear implementable solution that does not give a human player an unfair advantage.