Yes, this is true, but not my point.
My point is that when a guards commander is chosen there is little reason to get PTRS on penals. Even if both are weakened, it's not going to affect things like the viability of Guard Motor over other commanders. (I also believe the vast majority of instances of Guards being used is in conjunction with Guard Motor. 120mm mortars and self repair t34/85s attacking marked targets are no joke.)
good point