You are right for the standard eg. Ja! Product line, where prices are the same in all discounters. But Rewe and Edeka put many products that are available as housebrands with Lidl / Aldi out of their cheap product lines into their named brands for much higher prices. Examples are certain cuts of meat, cheese, etc. Look for example at chicken breast, which comes from the housebrand for a cheap price at Aldi and Lidl, is sold for much higher prices (Wilhelm Brandenburg at Rewe) for much higher kg prices. Same meat same package plant imaginary markup for walking to Rewe.

If you have to closely watch your finances and need to feed several people, you should never go to Rewe or Edeka, ever, period.