I'd love to see why you think warehouse work is harder, with more responsibility
I can buy that, on average, the work is more physically demanding (though there are similar jobs in stores). But the rest is almost certainly nonsense. Stores are directly responsible for generating revenue and profit (which, arguably, is the ultimate responsibility in any business). They also have to deal with a much broader amount of legislative responsibility than Distribution. Pricing, advertising, financial services advertising, a much larger amount of applicable food safety legislation, alcohol licensing, PFS, etc. Plus, there's customers, who basically wreak havoc from opening until close.
I wouldn't call warehouse work easy. But it's hardly complex or complicated, either. It's a tough job, but for a whole other set of reasons than those in supermarkets.