Alter mount types of planetary defenses so that they can only host heavy weapons or small craft
Is is to server two distinct purpose:
1. Make AI more competent at defending planets (medium weapons and missiles are just to easy to avoid/counter, but AI uses exactly these two types of weapons all the time for defense)
2. Resolve exploit of "besieging" a planet with a single heavy weapon until it is destroyed
This would also make sense lore wise as shooting with missiles and medium weapons into space is not very effective
Additionally: it might be worth increasing heavy weapon range for the above to be even more effective. I think railgun is in a very good place right now so should not offset the balance
In case missiles and PD is to be considered (no torpedoes those guys should only go for Destroyers
, I propose the following: have orbital defense stations that can mount these. This solution would not only spice up the invasion, but also considerably increase effectiveness of missiles, maybe even medium weapons could be allowed on these. Downside is that it would need art, but maybe the asteroid base could be re-purposed for this. Floating Platforms tech also lends itself nicely to this concept, and planetary defenses wouldn't need to be a funny 3 tier instant-upgrade system but two distinct systems independent from one-another.
Taking this even further: the 3rd tier planetary defense could be replaced with an improvement which can only host siege weapons.
All three systems would have to be researched and built independently from one-another and have their own icons in the build menu