Clarkinks has talked about disease resistance of pears in the past of pears like Warren, Ayers and Magness being super disease resistant vs say Comice which tastes good but is prone to everything under the sun. I think white gold cherry is supposed to be more disease resistant and black gold is supposed to be more winter hardy for cherries from what I have read. Years ago I tried growing pink popcorn blueberries and they all either came with a disease or got it soon after. You can grow apples that are disease resistant or ones prone to disease like honey crisp or pink lady. Those are some examples of what I am talking about by fragile. As I grow more fruit I realize the importance that Clarkinks talks about with pears. My disease resistant pears carry on while my Comice has been put in decline after a bad year. My super prone apples disappear from not coming back while my good apples stay.
I don’t mind experimenting on a very small scale with less durable varieties, but I want the bulk of my orchard to be of disease-resistant trees. In the case of pears, there are enough disease-resistant varieties that produce high quality fruit (e.g., Ayers and Warren, which you mention above) that I’ll hardly miss Comice, which likely wouldn’t last two seasons here. My mom planted Bosc here many years ago, and it died in no time, devoured by fire blight. All climates have limitations, and we have to live with them. To do otherwise is to waste time and money and to court frustration and burnout.
Sometimes, of course, you can’t be sure what will work in your area. And not all disease-resistant varieties will be disease-resistant in all regions. So experimentation—and loss—are inevitable in gardening/orcharding, if you do much of it at all. When we plant anything, we roll the bones—though we can increase our odds of success through careful plant selection guided by research (which has been much simplified by on-line resources such as this excellent forum). And in the end, you keep what works and abandon the rest.
To a large degree I think it would be a function of what is prevalent in the area you are growing them. If you are surrounded on all four sides by cedar trees with cedar rust you would be ill advised to push your luck with apple varieties that are not somewhat resistant. There doesn’t seem to be a lot of disease pressure where I am so I don’t pay attention to disease resistance when I pick my trees.
There are all sorts of tricks to do zone pushing; sometimes they work, sometimes they don’t. I managed to get a lapins cherry tree to limp around for 3 years. I even got about six cherries out of it before it died 
Disease isn’t the issue near Denver. Winter hardiness is much more so esp if planted in pots like you are doing. You need to know your enemy in order to respond appropriately.