Tell me, do garrisoned ships still have maintenance fees? Or are there only fees for ships that are flying?
I ask because I didn't seems to have as big of maintenance when I had ships garrisoned.
Anyways, the point is that having a military starbase and a planet, you must now have a fleet at both to protect them both. This means spending twice as long building fleets (and possibly twice as much maintenance). It's just not economical and it's not practical to have to double your fleet size if you want to build military starbases.
This isn't an issue for the other types of starbases because the other types really aren't worth upgrading so you only lose one module anyways.
Like maybe if your empire was surrounded by nebula and the only opening was guarded by a military starbase with the speed debuffs would it even remotely be worth it. But even then you're now just surrounded by clouds from which a patient enemy could launch a surprise attack.
Honestly I just use starbases for mining, and even then it's just for trading the resources away because having one ship with 3 fancy weapons on it is nothing in the scale of things. Starbases are really a bigger bane then a boon in this iteration.
There's nothing in the xml which seems to suggest they reduce maintenance costs. Starbases do give some influence, apparently (though I've never seen a non-influence SB increase it's border radius), and also give strategic repair bonuses along with ship range bonuses too. On larger maps, the range bonus is very important.
Not sure that I agree other starbases are useless; I build a fair number just for sensor stations (I dislike the gamey aspect of mega sensor boats), and economic starbases can be a huge boon if they catch multiple planets. On insane/abundant maps, the morale-booster module alone is a Godsend. Influence starbases are handy for holding borders and locking enemies out, and artifacts are equally very powerful. The value of mining bases is pretty much directly based on the value of resource buildings imo; these are currently really weak compared to the effort you need to expend to make them.
The big bonuses from military starbases mean that, by around 3/4 of the way through their upgrades, they reduce the number of ships required for the same damage output by 50% - meaning that eventually you're better off splitting a fleet in 2 and defending both than you would be otherwise (plus, more bang-per-logistics-buck while in radius). But you need to sink a hell of a lot of resources into the base to get to that level.
Combined with the range extension effect, the military SB seem more suited to a staging base for attacking the enemy from, than as a defensive base for your own empire. Don't build them in your own borders. Build them just outside your enemy's, stack ships on them, and upgrade them to hell and back. Then launch your fleet to attack from there.
I'd say that, generally, military bases need their progression reworked a bit (beef up some of the earlier bonuses a little more and tone down the later ones), the basic att/def modules should scale with tech, all starbases need a hitpoint-per-module bonus, and resource buildings need to be rebalanced upwards to make mining starbases more worth the effort (Thulium and antimatter being the priority here, with Promethium close behind - Duranthium is reasonable and Elerium is arguably OP).