88 individual guns that can jam, and can't be cleared until you land again. 88 individual guns that have to be removed, cleaned, checked, lubricated and reinstalled every flight. 88 individual drum magazines that have to be reloaded, manually. If we assume a very quick 15 minute field-strip maintenance & reload per gun, that's 22 man-hours of work every flight just for the guns, not counting the work needed to get them out of that contraption and then back into it again.
Wikipedia says the rate of fire of the PPSh-41 is 1250 rpm, so you're emptying that 71-round drum in 3.4s. An entire day of maintenance for less than 4 seconds of highly innacurate anti-infantry fire, basically just suppression fire.
Plus the effective range of the PPSh-41 is ~200m, so you're a nice low-flying target.
So yeah, your feeling is correct. This is a waste of time and effort, plus high risk for the airplane and crew.
Plus they are all pointing in the same direction. Is 80 bullets pointed at the same.spot any better than 10?
You would think three rows of 10 guns with the center row pointed down and the outer rows at a slight angle would give better coverage for less maintenance and be just as deadly.
I will give tacit defense of the Soviets on this abomination. It practically screams "fuck we aint got no bombs" and this was the result after finding a crate of PLSH-41s. Waste of time? Yes. Waste of manpower? Yes. Waste of effort? No. When in a rough spot ya throw shit at the wall and see what sticks, who knows maybe the R&D for this piece of shit led to something useful.