A market order is not a transfer of goods, it is only a form of communication to the other party that you want to buy or sell something. It shouldn’t take up to 5%(!) to just say you want to buy it.
All this does is make managing larger market orders a pain because if you first say you want to buy and the market changes you lose the extreme broker fees. It forces people to micro manage the same buy order into smaller chunks, which is tedious and ads nothing.
Broker fee should only be to prevent spamming the market. 0.5% or so is more than enough. The moment of actually payment should be the transaction itself and the transaction tax can be raised accordingly.
Give citadels the option of setting their own transaction tax instead of broker fee and have the same fixed broker fee for the citadels as well.