I don't think Rilisoft will be nerfing any weapons in the near future.
The Stalker (as it's called in the Wiki), is the most powerful mob in Survival, and it provides a good challenge in the game, especially in survival.
The Marksman M1 and M2 are modeled after a Steyr AUG, which is meant to be a light-machine gun, hence it's high mobility stat.