SM's are the default race, being the first type you encounter in the game. And yes, they are supposed to be the best of the best, but are they too good? Especially against the Imperial Guard?
No matter what, the only effective solution to counter a terminator deepstrike as imperials that I have found, is Karyskins with plasma. Sure it works, but what does that leave me on offence? And if I am on offence my base, no matter how many turrets, is screwed!
Nerfing the termies kinda ddefies the point of termies, and since after teir 2 turrets become mostly useless, perhaps have a 250/150 upgrade at the base which will "upgrade" the turrets from .50cal to .75cal (I know thats not what they are but just for reference...)