"Once it's turned with a bottom plow..."
That may be your answer, to some extent at least.
I would suspect that a lot of CUT and SubCUT owners don't have much (or any) experience with plowing, and may not work enough ground to make it worth learning. (My neighbor puts in a pretty good size truck patch with this Ford 3000, and he says that every year by the time he gets back in the swing of it and gets the plow adjusted, he's almost done. He's no "city kid," he farmed about 40 acres for years.)
I think that many of the CUTs and SubCuts are not well suited for plowing. They don't have draft control, aren't heavy enough, etc. That's not a criticism, it's just that they are designed to excel at other tasks.
Finally, even if you did plow with a modern CUT, can you handle (as Art suggested) a disk that is heavy enough to do a good job?
So, given a machine that is designed to do a good job with a tiller, you put a tiller on it and away you go!
Just my random thoughts here just before bed time...
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