Myth? It's a well-documented Russian tactic. They basically have a two-tier military at this point: competent professionals, and untrained expendable cannon fodder. Professionals are used to operate weaponry that's more sophisticated than your basic AK, machine gun and 70s-era armour. They are valuable because of their training and (at this point) a lot of experience. The second tier is used to conduct the kind of attritional warfare that requires far less training of individual soldiers or smaller-size units, and results in very high casualties. This type of offensive operation makes slow progress, the only real downside being the sky-high casualties, so recruitment and training adapted - take everyone regardless of health and age, and give them just enough training to accomplish something before dying. It's very effective if you don't care about the lives of these soldiers. The professional tier goes in to exploit a breach, mans the self-propelled artillery, flies the drones, etc.

I see you haven't watched much of how say Bakhmut was taken, or how entire battalion columns were destroyed business as usual.

You have to account for the possibility that for your enemy losing a couple of regiments for a town of 10,000 is acceptable losses.