People aren't happy when you are providing for their needs?
Weird, I guess the long list of civil unrest due to the people in power failing to provide food for their population doesn't apply 
At the end of the day you need an upkeep mechanic so you aren't getting a totally free power multiplication that can never be lost. They need food to be a suitable drain - giving them equipment increases their power and also increases their cost, food is simply a baseline. Having armour and guns will also help in fights, making it less likely for them to run, so it does factor.
Hmm, i can see your logic there, about providing for their needs, but they are not slaves as you have mentioned, and they are free to leave of their own free will, so they should be able to keep themselves fed and gather their own supplies if needed, but honestly as long as the value of their gear adds in to their loyalty score i'll be happy.
As for the concept that an upkeep cost balances improved power, it really does not balance it, take for example car insurance, you might be able to afford the base price of your car, but if you cannot pay the upkeep then your car is useless, just like the mercenaries which will flee if you do not pay the upkeep, effectively they are useless.
Now, lets look at the group of real life people who can probably afford a crappy car but not the insurance, to those who can afford both, those who have a steady income are those who can afford it, since they might not have a very high short term income, but as long as they have a medium steady income for as long as they own the car, they can afford it, now people who don't have a steady income have a hard time affording it, even if they make a fairly large amount of money when they do, since it does run out after a while.
Now compare that to the player base, we have the usual players who aren't that rich, and make their money in bursts, since they spend a few odd hours a week playing and gathering resources, but not steadily over a week, so they have to constantly keep farming in order to keep the resources needed to supply their junky slaves and greedy mercenaries and hungry companions.
And on the other hand we have bigger to medium sized factions who can support each other, and supply jet from TCing to the slaver who needs it for the slaves he has guarding the bases, and help share caps to fund mercenary assaults, and drop off old TV dinners they find to give to the guy with all the cool companions.
So in effect, you are not balancing the PvP side of mercenaries and slaves, but rather increasing the cost of keeping them, so that they are too costly to keep on hand for mundane use, and should be kept with the gauss pistols and other weapons for the big battles, but since they require upkeep, they cannot be kept and used effectively by people who only play a few hours a week.
And, finally, i think we can all agree, no one likes paying car insurance... in a game or real life..
-Ulrek-
