I like game design and probably should've gone into it. I like games that tell stories and the Gal Civ series has done a great job at that. 100% of my experience is with Gal Civ 3, but I will have to go try Gal Civ 2 someday because I've heard so many great things about it.
Something that frustrated me in GC3 was that I found it difficult to mix different hull types and my most cohesive fleets were made up of one ship type with maybe a support ship in the mix. Part of this is caused by the speed mechanic in GC3 and part of it is just min-maxing logistics. This led to many battles feeling similar to one another and I generally skip all but the most important clashes.
Mixing ship sizes would make fleets feel more varied and enriches the narrative/world.
In the current 0.65 iteration of GC4 I haven't yet found a need to combine ships of different sizes. I need to get a better grasp on the mechanics of combat though.
I think there might be a way to make mixing ship sizes beneficial and make it fit within the Gal Civ narrative.
My first idea was to make two versions of every weapon. One that targets tiny/small hulls and one that does more damage to large/huge hulls. In retrospect this doesn't really help and drastically increases the amount of customization the player and the A.I. do so it wasn't a great idea.
I think a better way would be changing how ship roles work. The ship role is something the player already had to set in GC 3 so it really wouldn't change the amount of work a player/A.I. has to do.
For this idea I would give each hull type 2-3 roles it could full fill with advantages and disadvantages to each role.
Dog Fighter - Damage buff against tiny and small ships, but damage reduction to large and huge hulls. Targets: Tiny>Small>Medium>Large>Huge
Bomber - Reverse of the Dog Fighter. Targets: Huge>Large>Medium>Small>Tiny
Multi-role - No changes. Target: Closest ship
Corvette - Damage buff against small and medium ships, higher chance to dodge. Targets: Small>Medium>Tiny>Large>Huge
Heavy Assault - Increased fire rate, decreased damage. Can help with attacks on core worlds if paired with a transport. Targets: Closest ship
Frigate - Increased fire rate, but large decrease in damage against medium hull and above. Targets: Tiny>Small>Medium>Large>Huge
Cruiser - No changes. Target: Closest ship
Making unique roles for different hull types specializes them without a lot of extra customization and would give me and other players a reason to mix and match different sized ships.
Anyway, food for thought.