Going from a model and sketches to a detailed design let alone testing and production is going to be a long and laborious project.
About as long and laborious as the detailed examination, disassembly, replication, and reproduction of the B-29 took. The changes in material, hydraulics, and wiring likewise required the Tu-4 undergo as extensive testing as a brand new aircraft would go through before being approved for serial production.
It is important to remember that from 1945 to 1950 the USSR had to spend enormous resources on rebuilding a devastated country, and also the integration of the occupied nations of Eastern Europe in to the Soviet sphere. By copying the B-29 the resources needed to get an interim effective heavy bomber were markedly reduced as well as having these in place when the USSR joined the atomic club.
The reverse-engineering of the B-29 was very much a massive investment of resources quite on the scale of the development of a wholly new aircraft. Had the Soviets not the resources to build, then they could not have reproduced the Tu-4. Nearly a thousand industrial facilities and research institutes were involved in the project. Disassembly alone was a immense challenge, since every step of the way each part had to carefully and non-destructively be extracted then determined whether it was a part unto itself or a subassembly of another part, and all in a way that left it completely unaltered for measurement. The fact that the bomber chosen for disassembly was not factory fresh further complicated matters, as the Soviets had to then estimate distortions on things like wing spars and fuselage joints and then do extensive testing to see how their calculations measured up.
The fact that in the early 1950s the USSR was able to get the Tu-16 in to squadron service within four years or so, does not scale backwards 5-7 years to the USSR just emerging from WWII.
By the early 1950s the USSR had made substantial recovery from the devastation of WWII, especially in areas like military design and production facilities which were prioritized in the recovery phase.
Again, this is unsupported nonsense. Soviet military economy has already recovered to pre-war levels by 1945, it was the civilian economy that needed an extensive recovery and in the industrial sector that was largely completed by 1948 (although the agricultural and service sectors would lag into the early-50s).
It is also worth remembering that Soviet jet engine design got a huge boost not so much from captured Nazi engines but rather from the RR Nene sold to the immediately following WWII. Another example of a tech jump start.
I can find nothing in common between the Tu-16’s AM-3 and the Nene.
Again, it is not so much that the USSR could not have built a B-29 equivalent, or decent jet engines absent these sorts of transfers, just that getting them accelerated the process substantially. Just like the atomic bomb, the spy information did not transform a hopeless program (like the Nazis had) in to a viable one, rather it eliminated a lot of the false leads and duplications making the jump-started program more efficient.
I’ve already pointed out how fast the atomic bomb spying accelerated the Soviet nuclear program. Assuming a similar accelerative timeframe, that still puts the Soviets ATL domestic bombers first flight in 1947/48 and operational service in 1949/50. This is ignoring that the Tu-4 program began slightly later (about 5-8 months, with progress having gotten as far as the wooden mock-up stage at about the 5 month mark*) after the original ANT-64 project it terminated.
*Interesting comparison here: the Tu-4 didn't reach wooden mock-up stage until December 1946, 18 months after the project began.
Performance was poor on the Stal-7, that got Bartini sent off.
Kurchevsky got arrested for working on a helicopter. During the Purges, he was charged with designing poor weapons, the recoilless rifles, and was shot.
Bartini was arrested on dubious charges of spying for Italy, with some bogus charges of sabotage (among others) tacked on as a after-thought. He never saw a work camp though: he was immediately put into a Sharashka, basically a research camp, where he worked on the Yer and Tu-2 bombers. Still nothing about being punished for working on unapproved projects.
In Kurchevsky's case... well there's two different cases there. The 1924 arrest was done not because he worked on a helicopter but because he embezzled state funds to do so. Regardless of your thoughts of engineers working on unapproved projects, I'm pretty sure you would agree that stealing money from the government to do so is a legitimate crime. His 1937 arrest and execution likewise came from the fact that his
approved projects had proven to be irreparably defective, not that he was working on unapproved projects, even if that's still a shitty reason to execute a man. The fact he was a close associate of Tukhachevsky, which was a very politically problematic place to be in late-1937, probably didn't help.