Are you putting feeders outside hives? That is what I get from you original question.

Do you like sugar water better than honey? Bees don't either, and, outside the hive feeding is just the perfect way to create robbing impulse.

Hive top feeders will be better, 1 per hive and everyone is happy, with plenty of feed.

This is how I do it: (contraversial)
Do not feed bees......feeding bees promotes poor genetic stock to survive the winter and swarm in the spring. (giving you poor drones for your virgins to mate with)

Letting bees which rob hives survive does the same thing.
It promotes poor gentic stock.

Each time a hive swarms there is a virgin queen who needs to be mated with stock which has the traits you are looking for. Each time breeds with undesirable traits get out there, they are providing drones with poor traits for your virgins to mate with.....causing the cycle to go on and on.

Why do you think mite resistant bees came from an area of russia where there are no beekeepers????

Because no one treated them with miticides, and natural selection took over. Now we (Americans) are importing Russian Queens to try and fix what we broke in the first place.

Natural selection has been my best friend.
I choose overwinterin bees. (I have never fed 1 colony)
If they make it without feed they are good bees, and are allowed to continue in my hives.....providing queens and drones..
Over time I have saturated the area with good mating stock.
I currently maintain 60 hives in N.E. Ohio and have averaged less than 20 percent loss.
However my counterparts loose 30 to 50 percent of their hives each season. (even with feeding)
Just keep allowing those feeble bees to survive....I will still be here in 10 years. They will be fed up with the cost of replacing bees each year.

I do not treat bees for any disease other than for Varroa Mites. I use formic Acid.
I want to get closer to not treating for even mites.
I have an "experimental yard which gets treated 1 time a year (fall) rather than 2 times spring and fall.

I treat this yard the same as all of the others and I have experienced slightly higher loss due to higher mite concentrations. It is my belief that over time these bees will develop resistance to mites and miticides will someday be a thing of the past for me.

What I was thinking, along your lines, is to add some other race of bees in to the mix- perhaps it will, over time, quell some of the robbing instinct. On the other hand...you eluded to the fact that bad beekeeping will promote robbing. Yes, that would be me. I have done every possible wrong thing this past season; I graduated from the school of hard-knocks with honours.
So, with all my kill-outs, I have the need to re-fill my hives. Maybe this would be the time to add the new blood.
I have some monster hives that need to be split- that will fill up some hives but then I still have some empties.
BTW...I really appriciate your taking the time to write such a great entry. I paid very close attention.