Yes, they were defending in an urban area, but I think this matters less than you might expect. Russia's strategy was to saturate the Ukrainians with artillery, and they undoubtedly have superiority in this area. This kind of warfare basically negates the advantages of urban defence. Sure, it took a long time to make progress, but by design it limits the casualties of the attacker. I'd wager that most Ukrainians that died there never even saw a Russian solider.

Truthfully, no one really knows how many died (on either side), but Wagner stayed in the field vs 50-odd Ukr. brigades. How do you reconcile that with a favourable casualty ratio?