As you pointed out, actually capturing the city was unnecessary. But having captured the city, Hitler was very determined to hold onto it. Abandoning it would have presumably meant having to recapture it later; and once again suffering that same 1:1 ratio during the recapture.
One thing I’m wondering: why would Germany have to (or even want to) recapture at great cost a city that it was unnecessary (and indeed counterproductive) to capture in the first place?