I still am not clear on a few things:
The lever. If you lift it will add extra stress due to the extra length. At the same time you are not using the plow to lift, but push. If you push straight with a long or short lever it probably comes out pretty much the same. If the blade is not angled this would seem to be the case.
I would imagine that there is less force on the closer in side of an angled blade than the other since it is releasing snow off to the side but I am not sure if that is the case. At any rate, I could see how if the force is unequal and the lever is longer it would magnify the difference. That is the only way the longer lever seems to make a difference???
Since the plow is generally going to be sliding on the ground, with most of the weight supported by the ground, would it really un-weight the rear tires that much?
RTFM:
(tractor) front end loaders are NOT designed for it, especially the little ones.
SOMEWHERE in the loader's literature there is a paragraph or two explaining that the loader is for moving light material ONLY; it is not for gravel, stone, etc., not for digging, not for dozing - and if it is half decent it will explain how to always drive into the pile straight on in order to avoid tweaking the frame, though it may not explain that frame tweak is the reason (-: