Except that trade hubs based in citadels have distinct advantages over those based in NPC stations.
The only difference is the potential broker fee, which for trade hubs in citadels can be as low as 0, while in NPC stations the lowest is around 2.25% or so. However most if not almost all of the trade in jita happens in IV IV, not in perimeter in the citadel. You lose a small amount of margin profit yes, but that’s the price for the 100% safety of the NPC station.
By “simply living out of NPC stations”, you’re forcing smaller corps to lose out on the fees earned from citadel trade hubs, and you’re forcing them into less-appealing trading positions since their fees are inherently higher.
Losing the tax revenue of the citadel is the price for being unable to defend them, there are other ways for groups to raise revenue such as taxes, donations, buyback, or mining/pve ops that donate revenues to the group etc. And the difference in NPC tax vs citadels is slight, and can be significantly reduced with standings and skills.
This cuts into their profitability exponentially; lower income and fewer sales.
I disagree that a 2.25% or so broker fee is an exponential decrease in profit, even if someone spends the effort to kill all citadels in highsec, you can live out of NPC stations without a problem.
What you described is precisely how you lock down hisec (at least from a trade standpoint). And nullsec blocs are starting the process already, even without capital ships in hisec.
I disagree, worst case scenario you pay a few million more per industry job, and 2-4% more broker fees to put up buy and sell orders. You may run into issues with moon mining if the athanors keep getting attacked, but you can drop a single athanor per holding corp and make them pay constantly for wardec fees, and form an wardec alliance to ally with your structures and defend them.