a fighting position is a static position, and youre not always gonna manage to put one up to cover a flank while youre advancing. thats the benefit of the 50cal team, you can constantly reposition and help cover new approaches where as the fighting position cant. also i trust MG teams in green cover since its pracically impossible to wipe a full health squad in green cover with one mortar or grenade.
Just to be clear I never said 50 wasnt better as an aggressive MG. Im agreeing with you in that sense.
But im saying would you want a .50 cal defending your cutoff/flank (Like kharkov cutoffs,Kholodny ferma cutoffs) or a fighting position. Thats the "Flank" im talking about.
Id hope you'd pick spending a little bit of manpower and munitions over wasting double the manpower and ~7 pop cap,in a faction thats starved for manpower and popcap.
And regarding the nades...maybe your lucky and havent lost a game due to a .50 getting blasted by RNade or GrW 34 and then finished in one burst of gren LMG, and it then being turned and used on you.