Regarding the low precision of the bombing and impossibility to destroy the Soviet factories. This theory has been disproved by history.
Please see my earlier comment:
WW2 bombers. If Germany had the allies heavy bombers would they have won the war?
The number of engines probably was not the most important factor, since the above-mentioned operation was done by He 111 and Ju 88. And carefully planned but never fulfilled
Eisenhammer was to be conducted by Mistels.
Some more about the precision - an episode during the Operation Frantic, quoted from Wiki:
"On the night of 21 June, the Combat Wing of B-17s which earlier landed at Poltava sustained severe losses in a German air attack. ...
For almost two hours, an estimated 75 Luftwaffe bombers attacked the base, exhibiting a very high degree of accuracy. Nearly all bombs were dropped in the dispersal area of the landing ground where only B-17s were parked, indicating without question that the B-17s constituted the specific objective of the raiders.
Of the 73 B-17s which had landed at Poltava, 47 were destroyed and most of the remainder severely damaged. ...
The stores of fuel and ammunition brought so laboriously from the United States were also destroyed. Three days after the attack, only nine of the 73 aircraft at Poltava were operational. ...
Red Air Force losses included 15
Yak-9s, 6 Yak-7s, three trainers, a
Hawker Hurricane, and a VIP DC-3. ...
The well-planned German attack was led by Oberstleutnant
Wilhelm Antrup of KG 55 and carried out by
He 111Hs and
Ju 88s of KG 4, KG 53, KG 55, and KG 27 operating from bases at Minsk. The operation was nicknamed
Zaunkoenig. After the He 111s left, the Ju 88s strafed the field at low altitude.
He 177s from Night Reconnaissance Squadrons performed target reconnaissance, pathfinder duties and bomb damage assessment. There were no German losses."
Operation Frantic - Wikipedia