"For example, in my area if I don't treat for mites, the bees are overun by September, and most hives die. The presence of large numbers of commercially run hives no doubt has some influence on the situation."

I just wanted to respond to just this part because there are some effective non-chemical varroa mite treatments.  Take for example the Screened Bottom Board with the Small Hive Beetle oil pan underneath.  Or the powedered sugar mite drop.  Or drone brood kills.  If you're doing all that and the mites are still taking over, then you might have to treat for them, and/or breed from survivor stock to try to get bees that pick mites off each other a little better.

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