John Erickson was a great historian, but he was not necessarily an unbiased one. When he first approched the Soviets to access their archives, so the story goes, they didn't trust him. He had to provide some bona fides. He told them that his wife was Yugoslav, presumably also pro-Soviet. They went and checked her out. They approved of what they found about her, so they opened up their archives to him. He had an abundance of information to work with. However, it seems that one condition of allowing him access to their archives was that he should not write any history critical of the SU, the Red Army or the GPW except where they allowed him to for their agenda.
His work in this respect is very similar to Glantz's work. Glantz is now a memeber of the Soviet/Russian academy of sciences.
It is always helpful to have this kind of awareness in mind when assessing an author's work.