That's through sheer necessity, as the AI lacks the skill needed to win in Muscovy's real life situation. As bad as railroading may be, you need to at least make it possible for what happened in real life to happen in the game as well.Muscovy was, at their very worst in EU 4's patch history, still stronger than its real life version by a margin in 1444.
DotA-style balancing is not necessarily bad balancing.AI choke jobs are no reason to overstack a starting position; if you did that every nation would be stacked and it's back to square one.