Drives should also have a cap. Giving Constructors loads of drives makes them too OP compared to moving shipyards.
Or, you know, don't do that because it would be silly.
I don't have a problem with scaling engines. A 1 ton car needs a lot less horsepower than a semi. That said, perhaps stages of scaling would be best. There is a reason nuclear engines are rare on ships.
This, IMO, has always been a weak point in GC games. A smaller version of a weapon SHOULD give less damage. Some weapons should not be able to be on a small vessel (coastal boat with a ICBM?, please)
That said, a vulcan cannon can be placed on a smaller vessel.
However, this is all grognard stuff.
To keep it simple, don't scale anything. If you want to armor a capital ship, you need X amount of armor vs a tiny vessel. Shields, you need X amount of power + shield generators. Chaff you need much more for a large vessel than a small one. However, point defense is a fixed size. So tiny vessels can only knock down say one missile while a capital ships my knock down several.
Again, just my opinion
<edit> oops, back to the original topic. This has come up other threads and I still believe stacking should not be allowed. I do like the idea of a long range vs short range sensor though! </edit>