If it seems good on paper, it will be a nightmare in game. You'll rush the LMG squad with your SMG one and finish with a 4 men squad alive but almost wiped out and still didn't inflict any damage, in close range and fucked up because you can't anymore retreat - not enough hp and the deadly LMG accuracy at short/mid/long range, it will just be a lose your squad Run just to get the possibility of what, killing one model of the LMG squad before being wiped out? Better having the actual gameplay, at least you are not going to intent stupid actions because you see your squad models still up during the run.
LMG maximum area of damage must be short as SMG one, one works on far range, the other works close range. Nothing less nothing more. At the moment a squad move from the area of damage, the dps dealt to it must become ridiculus as for SMG dps.
If it is not what it was in real life, at least it is balanced.
The concerns you mentioned are addressed, discussed at great length and answered quite satisfactorily in the linked thread.
You shouldn't be charging LMGs across open from long to short anyways, and though you would suffer more general hp attrition from Cruzz's change, you will arrive with more models intact, and hence a better remaining DPS, than if the LMG fire was focused on one model at a time, ripping it to pieces, and denying you that models weapon DPS upon arrival.