Eh. Doesn't demand matter too? Comparing Toronto and Montreal, we've got arguably better farmland here, but they've been miles ahead of us until very recently. But there was no demand here, of course.
I could easily see the lack of the demand side hurting the mid-west (outside of factory farms), even if the growing conditions are better. Consumer and restaurant demand in the North East has certainly helped better farms. Not just hipsters moving to the Hudson Valley, but long time farmers being able to expand their business.
Not to say that the MW is better - I have no idea - but it's not obvious to me that things are necessarily better there just because the weather it. Take Florida - it's a produce wasteland.