But when duplication was associated with nuclear weapons it was all different. The USSR went the great lengths at super priory to copy the early US work and the B29, including the battle damage repairs, became the TU4.
That is true. The Soviets were impressed by American technology and did their utmost to copy it from the early 1930s onwards. Germany in 1945 had no effective strategic bomber and designs like the Ju 287 must have looked pretty advanced which meant long development times and they might not work out. In the B-29 they had a proven design.
We also have to remember that Stanislav Shumovky had literally smuggled out planeloads of intelligence on US aviation. The Soviets had been acquiring information on the B-29 since Rickenbacker's visit in 1943, even before that they had obtained a B-29 blueprint. So the planning went back a long way. The systematic copying of its airframe, materials, avionics and engines was impressive, no German design had equivalent impact in terms of a complete revolution across every component. The only German parts of the Tu-4 were things like the IFF system as the US had tried to prevent any radar technology getting to the USSR. Shumovky had already worked out metric conversion tables and doubtless much of the information he sent must have been invaluable in attempting the project.
It kickstarted the Tupolev OKB for sure, soon after many developments and derivatives were on the drawing board. The difference was probably the quality of the designs, Tupolev's team were no amateurs but they could now save a lot of development work.
Saying that, attempts to copy the F-86 quickly foundered, they knew they could do equal or better themselves and Sukhoi's OKB was reborn. The U-2 copy by Beriev never got far either, Zubets worked on the engine technology but it doesn't seem to have led to anything.
Copying American designs was probably less politically problematic in the Stalin era, the copies came from captured material, they didn't have the stigma of needing foreign designers, they could be dissociated and there had already been copies and licence-built American aircraft and engines since the 1930s (Catalinas, DC-3s, Vultees).
The Soviets pre-war had brought British, French, American, German; they had already been copies and licence-built American aircraft and engines since the 1930s (Catalinas, DC-3s, Vultees). Ship designs came from Italy, Christie suspension for tanks. In many respects the Stalinist rearmament was internationalist. Stalin maintained this during the remainder of his life, he used German know-how, brought British jet engines, copied US technology. He took whatever he could buy or steal for the technology which they could build on. He wanted rapid rearmament, he didn't want to wait a decade for R&D to bear fruit. Foreign technology was the booster that his engineers could build on and adapt, it was building blocks. Had the Cold War not chilled so much so fast its open to speculation how much other technology might have been acquired from the West.
Arguably for all their loot and plunder, Germany actually made rather poor use of the aviation resources they captured. There seems to be little evidence they were interested in French research for example, later they gave French industry menial tasks like designing sub-components or civil designs or one-off prototypes but they were hardly tapping into the resources fully.