What is not a myth is that brass washed steel and steel casings don't seal the chamber as well as pure brass because they dont expand as quickly as brass.
The result is the components in your reciever are being subjected to pressure and carbon (etc) to a greater degree than shooting pure brass cases.
How do you know over thousands of rounds your reciever is just going to take it? It might, it might not and wolf is far from ultra accurate.
For my nickles worth Im not dumping bargin basement ammo in my mid to high price anything, cheap has its places but for me its not here.