Not to mention zerk counterparts all run slam to add to their utility, I don't think having side stun would be unreasonable especially for smallman/solo play.
Unless I missed something within the last few days Dual Wield doesn't have a side stun opener.
Although, as currently stands, I agree that access to 9s stun through slam puts mercenaries and blademasters above the berserker.
I have no issues with LA earning a side style stun; I would however like to see it in the low level 30 range. Mercenaries and Blademasters do have to sacrifice weapon skill and damage to earn slam.