It may be true that I do not understand whatever nondescript fundamental issue it is that you mention but don't elaborate on, but I most definitely understand the constraints of farming. Being a farmer, I live it each day.

And as a farmer who owns equipment from across all the major brands (and some unheard of brands to boot), you are right that John Deere is most reliable for having parts in stock. I've been burned by the others having to wait a week on parts to be delivered from who knows where. That is not a fun position to be in. Repairability is where John Deere has the clear advantage. That is, just as you point out, why they are most popular. Nothing else matters if your equipment doesn't work.

You pay a lot more for that luxury, but when the clock is ticking...