That exists across the game.
No it doesn't, not to this degree. Very few choices are as black and white as "take AC on a 2-dice ship".
Besides those that are more imaginative might find a combination that others don't see.
They really won't. The gap in power between AC and any other choice is so huge that no plausible amount of creativity is going to overcome it. Taking anything but an AC would be about as smart (and about as common) as taking a hull upgrade on Whisper/Echo instead of ACD.
So the better question is why bother restricting it?
Because you want more control and the ability to fine-tune the ship instead of leaving it wide open for whatever future upgrades FFG decides to release.