I've noticed the behaviour you describe across both allied and axis forces in Final Blitzkrieg, so it is not confined to the Russians I certainly didn't notice the problem of a team, or individuals staying outside of a building until the introduction of Engine 4. Some people had in the past complained about "squads" bunching, or moving in single file. So rather than splitting them into "teams" and avoiding the bunching themselves, they wanted the behaviour changed by BFC, or at least that is how I read it at the time, I maybe wrong on that score. I don't know if the hanging around outside of a building has been addressed in either patch 4.01 or 4.02 as I now confine myself to playing on engine 3.