Are you comparing the cost of strictly identical products or something else? I'd be very curious to have some sources if you have any

No - small shops tend to sell mostly expensive branded products in smaller packets, whereas superstores sell larger packs of unbranded products.

In my country and city the small shops are largely stocked from buying the same things from larger shops combined with their own resupplying network. So you can either walk 100m to the corner shop, pay couple dozen % extra or walk 500m to the nearest Lidl or similar and save on basically the same products.

I would think the sensitivity to this would depend a lot on family size. Shopping for just myself... it doesn't matter much. Shopping for a family of 4 would be very different.