Good article. Well written too. The basic summary is that cat kibble causes diabetes and maybe other issues such as IBL.
Another item is not mentioned. In the old days with cats in the barn, they also probably just died when they got sick. They probably did not get vet care. Or if they did, maybe their disease wasn't known.
My great grandparents died in the 1950s. No one knew why. They just got diseases and died, cancer and such. Same kind of deal.
In a recent thread I was wondering about insulin for cats, and when it was generally available - basically in the mid 1980s. Before that, cats basically just died if they had diabetes. Sure there may have been some small percent that got treated. But most diabetic cats probably just "got sick", then died.