I suppose you would prefer to have someone carry that fifteen pound beast you’re imagining, too?
Rifle itself is less than 6 lbs, with 2 more pounds for 40 rounds of 7.62mm. If you want to carry spare barrels, and more ammunition, well that is a bit heavier. Having some extra weight in the barrel for a 7.62 version is not a bad thing. Happy thing about bullpup design is the heavy ammunition weight is close to the body, so the weight doesn’t shift much as you empty your mags.
One argument for the BAR vs the German MG-42 is weight. MG-42 with one minute of suppressing fire would be 25 lbs for the MG and 100 lbs 1400 rounds, and and another 6 lbs for a spare barrel, 131 lbs total.
BAR is 19 lbs, with 240 rounds for one minute of fire is 15 lbs, for 34 lbs.
Of course in a defensive situation the MG-42 would be superior.