The analogies used here are a bit off.
Fortresses in the real realm were built in strategic locations, and if there wasn't one, made the strategic location of the region to defend holdings. Later on castles were built to maintain claims on land, and we're built in more defensible locations on said land in order to maintain the claims as well as project power from the claimant on his subjects.
Static defenses are a meaningful part of warfare. Not all static defenses are Fortresses or any analogous object to one. Sometimes the battle makes a city, a series of streets a river or other thing a strategic defensible location and static defense is propped up there.
What I'm saying here is, that static defenses, and fortress systems should very well be in this game. Like SoaSE, you could make a near impenetrable system, but again that's a cost. Ww2 has the maginot and siegfreId lines, the Atlantic wall, etc etc.
Direct assault of defenses should cost more than just a few days of game time before they're destroyed. They should be relatively expensive (maybe not each station, but the series of the objects used to fortify said system be it multiple stations etc) to the defender. The biggest flaw in space games, is defenders rarely get any kind of advantage. While attackers should have initiative, defenders should have the advantage of local supply and defenses in their favor. Now those are things not in here, but being able to steamroll stations so readily is.
This is more a symptom of the epically shallow combat system we are given which amounts to put guns (or lasers or missiles if that's your thing) on ship, click on thing, make dead. Rinse. Repeat. (There's more to it but that is basically the gist) the problem is the lack of other game elements currently (a vibrant economy that's more than just 2 resources, diplomacy, espionage, factions et al) to fully flesh out the combat system because without a more complex economy, the map painting isn't really useful after the first couple of wars(just more stuff coming in). Without that slight complexity, you really are not compiled to defend much, just pushed to pop the fleet of your war subject and then mop up. Sure if you're weaker, popping shipyards and whittling their fleet down can turn the war, but to even the average player this is almost never the case.
Point is, combat in general needs altering, more than the stations need a buff. If combat would be more complex in its executions and such, then you can tune stations to fit the niche they are meant to in a space game: a static deterrent. You either go thru the station and deal with that, or spend loads of time going around it to deal with it later
In stellaris, we just completely ignore it... and chuckle if we stumble upon an ai one