I'm not sure I agree that Bastions are targeting the wrong side of the DM screen- one of the big failings of AD&D was making players actually care about the ability to create bases and gather followers. In 2e, especially, I saw plenty of level 9 and up Fighters who never bothered to establish a keep because they didn't really see the advantage- the force you acquired was very small, not sufficient to really go to war with anyone, and generally was enough to protect the keep itself. The 5th-7th level leader character was the only cohort worth mentioning and for groups that wanted to tackle more and bigger adventures, which became more prevalent in 2e, they might quickly lose relevance anyways. Contrast all this with the upkeep (heh) of the keep itself and the fact it ties you down to one location, when most adventurers travel far and wide over the course of their careers.
I knew a lot of DM's who didn't want a lot of miscellaneous NPC's hanging around to complicate their games to begin with. Then add the fact that the Stronghold Builder's Guidebook was a later addition to the game, like the whole idea was an afterthought.
The Dark Sun Fighter was in a similar position- they were always intended to engage with the Battlesystem sub-game (just as D&D was meant to transition into Chainmail), but I have to assume groups that did so were rare, as I never encountered one.
So the strongholds of old really were more useful to the DM than the players, in the form of giving them something to make the players care about ("While you were away on the Astral Plane, an evil duke usurped your keep...") that many players didn't think was worth the effort to have in the first place, which is why all this stuff became optional in 3e with very little fuss (amusingly, in 3e, Leadership was one of the most busted things you could allow a player to have).
So you have to make the players care about the Bastion system or they'll just...not have Bastions. Is making it an alternative power track a bad idea? It's hard to say, since the whole point of this exercise is to make treasure valuable again. Right now, D&D characters are in the same boat as the billionaires of our world "gee, what do I spend my money on? I have all these holdings, one mega-yacht for each ocean, summer home in the Hamptons, winter home in the Caymans, I have a private jet, maybe I'll try to go to space...". That's cool and all, but it doesn't tie into the game itself, where it's about going on dangerous quests and fighting powerful foes.
Players rightly note that money just lets you buy things- power is what lets you do things. So they naturally want a way to turn money into power.
Now, one might say "but James, money is power!" and yes it is, to a point. It's narrative power in the setting; you can prop up kingdoms, fund revolutionaries, hire mercenaries, etc.. But not a lot of games unfortunately revolve around the setting as more than a backdrop for the adventures players go on. You'd need a whole book to show DM's how to make their setting matter to the point that players will directly engage with it, at least- there's no way a subsystem which at best will fit into a chapter can do that.