To recap, my conjecture is that decentralized power for PCs (i.e. power outside their immediate bodies) faded for a while due to desire for character immersion coupled with a desire for simulation. I expect the GM not wanting to handle dozens of NPCs that the immersive-driven player no longer wanted to handle had something to do with it. In fact, mechanics has a big part in bringing them back, at least for me.
Some steps back were pretty easy - having players spend character resources to get iconic/signature gear that works better than normal and can't be permanently lost was common in supers games but worked its way into others (Earthdawn's magic item system was built around linking you to your magic items in a way that both made them more powerful as you got more powerful and forced PCs to research the setting background for plot hooks...alas like much of ED it was a little too complicated for casual play; Feng Shui lets gunmen and martial artists have signature weapons they can't lose, etc.). That's all to the good, but it's not quite the same as having the power a of a local lord with a mass of troops that 9th+ level fighters got in early D&D.
Several games do let players buy rank in organizations and higher levels of resources for their PCs, but usually make control of those organizations cost prohibitive and find ways to minimize what resources can do (because hiring a team of mercenaries to take point on your battles is what _villains_ do...). A revelation for me was the Big Eyes Small Mouth system for Organizational Ties, where control of powerful groups was in reach for players - mind you those powerful groups were sometimes student counsels and the like depending on the game - as were groups of flunkies. In the playtest for Silver Age Sentinels Org Ties these really came into their own, where for the cost of a mid range energy blast you could make your character, say, Director of SHIELD or in charge of Wakanda.
Yes, these still required GM buy in (a surly GM could then try to force you to buy a countries worth of flunkies and massive resources and tons of agent level fighters) but it put the idea of playing a character who controlled a large, powerful group back in reach of the players. The idiom of the game still required that, like the Steranko Nick Fury or Christopher Priest's take on Black Panther, that the hero lead from the front, but that helped bridge the gap between immersive play and massive resources.
Later games, like FATE, reduced everything into Aspects that can be invoked in play, and that aspect could just as easily be 'Lab of scientists and flunkies' as it is 'genius scientist' as both let the PC do sciency stuff. That's even better in some ways as it pulls everything back into a single mechanic.
Which is what I was trying to go in Gaslamp Romance. I'll talk more on Monday as to why I did what I did for that and how I hope it will work.