While what you're saying is basically true, what it explains is why the earthy words in English are Germanic, not why they're short.
Earthy words are short in French too. "Merde" is as abrupt as "shit." And German is full of long words.
What's really going on is that earthy words tend to be short, whatever their origins. And since English is not so much a mixture of Anglo-Saxon and French as a core of Anglo-Saxon with a veneer of French on top, the earthier, more basic words in English tend to have Anglo-Saxon origins.
Earthy words are short in French too. "Merde" is as abrupt as "shit." And German is full of long words.
What's really going on is that earthy words tend to be short, whatever their origins. And since English is not so much a mixture of Anglo-Saxon and French as a core of Anglo-Saxon with a veneer of French on top, the earthier, more basic words in English tend to have Anglo-Saxon origins.