Such a statement can be applied to any scenario of combat. But the specific claim was that the purpose of Bakhmut was just to serve as a meat grinder for Ukrainians. But here, Wagner is explaining that each house is a fortress and it takes them days or weeks or months just to take a single house. Such situations indicate high attrition on the attacking side, which also explains why they complain of being low on ammo and everything else.
So, who to believe? The Putinist arm chair generals, such as yourself, fantasizing about Russians killing thousands of Ukrainians at their leisure, or the actual Russians who are giving excuses for their dismal failure to take Bakhmut after more than 3 or 4 months of combat?
Back in the ‘80s in Berlin, we assumed a 10:1 defensive advantage against the Soviets without air superiority and a 48 hour build time for defensive positions.
Each hour raised that quotient as defensive positions continue to harden until moment of contact.
96 hours into conflict, many parts of the line (canals and straight sided obstacles), the defense expected a 100:1 advantage.
No sane army wants to be the offense in MOUT.