So maybe at least part of the build-up you suggest may not entirely be the bees' fault.
I saw the same I had 2 good years... and those good years made it hard to change my ways even in the face of 3 years of 100% losesI have read the anecdotes and know more than a few beekeepers who have initially met with success in a TF context only to have significant failures after a few years.
you see the same pattern in a lot of organic AG programs ..specifically common in aquaponics (fish waste hydroponics) systems, you set up with no dirt no weeds and no bugs and it takes a few years for the pests to drift in and reproduce at a scale that's a problem.. and much like 2 and 3 year beekeepers they think they have to problems licked... till they don't
I remember a "great idea" locally, a large active thermal battery earth mass greenhouse .. run fans to suck in hot air in to the ground during the day and cool it and put it back into the greenhouse, at night warm air from the mass heats the green house... seamed great till they caught a powdery mildew infection and there was no way to sterilize the mass.. took a bit to get the reason figured out . even years later if they tried to turn on the fans there was an outbreak.. end result fans off, great idea dead
I am going to pull a GWW here... "some were that I can't recall at the moment " there is a Skep keeping reference that one sould not by a stock that was XC old (I want to say 4 years) as it won't do well do the old combs ...