This is something with all the expanded mods but the base defenses structure still feels underpowered. It just doesn't do productive things and most of the time it's still better to have production buildings instead. I think the base defenses should be given garrisons of their own. Maybe even just copy/paste the ones of the tax buildings. Base defenses is a very niche thing cause of how the game is. Ground battles can be bypassed and of course base defenses don't have any value in grand strategy. So since they are so niche they should be very strong in the situations where your opponent is forced to take a planet with those things on it.

Personally I think they should be given much stronger garrisons than the tax building cause I feel often in ground battles they don't actually make a successful defense more likely. They mostly just make ground battles longer but that only has value if you have large garrisons cause you can use them to grind down the enemy. That's why I think ground defenses should be given their own garrisons cause otherwise it is pretty pointless.