Yes if your entire society relies on one staple crop that has low diversity and no pest management, you are at high risk, but that is not modern society.
If the cavendish is wiped out, people would barely notice. Even if it happened with corn, it would be disruptive, but not catastrophic. Our food system is too diversified to really collapse from one disease.
Doesn't mean that specialization can't have obvious benefits.
The Irish Potato Famine happened because their potatoes were descended from a single handful of potatoes. As a result, a fungus that affected one potato plant affected every other potato plant. About a million people died from that.
The corn blight in 1970 resulted in the loss of 1/3 of the US corn crop. If the weather hadn't broken, up to 85% of that year's crop could have died. 85% of the seed grown back then used Texas Male Sterile Cytoplasm as part of the hybridization process. In response, the US government created and continues massive subsidies for corn production. This is why high fructose corn syrup is cheaper than cane/beet sugar, and why HFCS is so widespread in US food production.
One book that covers the history of monoculture failures like this is Altered Harvest:
https://www.amazon.com/Altered-Harvest-Jack-Doyle/dp/0140096...
One book that covers how prevalent corn is in American food production is Omnivore's Dilemma.
https://www.amazon.com/Omnivores-Dilemma-Natural-History-Mea...
The banana flavor used in candies tastes nothing like Cavendish bananas. That flavor was based on the Gros Michel variety that went economically extinct in the 1950s.
its quite unfortunate as srilankan coffee is quite good and tragically under appreciated. most locals will serve you nescafe as they think its "fancy"
>...This is why high fructose corn syrup is cheaper than cane/beet sugar, and why HFCS is so widespread in US food production.
As you point out corn subsidies lower the cost for HFCS, but the US also uses import restrictions to keep the US sugar price much higher than what it is in other countries:
>...The US sugar industry receives enormous government support and protection from foreign competition. The sugar program has changed over time, becoming a complex set of rules developed to promote sugar production primarily at the expense of domestic consumers. The program has also affected foreign producers and consumers through import restrictions that have significantly reduced the world sugar price. Since the mid-1970s, as a result of the sugar program, the price of sugar in the United States has been almost twice as high as the price of sugar on the world market in most years.
https://www.aei.org/wp-content/uploads/2011/11/-sweets-for-t...
The little farmer who grows a variety of crops is out-competed by the corn growing neighbor who has relatively cheap specialized equipment and seeds available to allow him to work ever larger and more productive fields for year after year. The little guy ends up closing shop before the neighbor gets wiped out by some highly specialized pathogen. As John Maynard Keynes noted, "Markets can stay irrational longer than you can stay solvent." Monocultures might be a bad idea in the long term, but for immediate profits they cannot be beat.