Lou, it's my theory that your last sentence describes their success and longevity. They were overbuilt. And they rarely operated at 100% capacity. In today's attempt to minimize production costs and increase profit margins that "cushion" is missing. I expect my Kubota to perform tasks regularly that are at or near it's capacity. In our attempt to do more with less we have put the longevity of our modern tractors at risk.
I do not think this theory is as applicable in the large AG class tractors. But it's common practice in the Utility class and smaller.
I also agree with you concerning simplicity. My 1984 Ford 3910 is built with that theory. I recently purchased a 1984 Ford 555A TLB. It's the same.