The issue was less about what they could pilfer and more about what they could actually use. Soviet-era industry was simply too inefficient, outdated and uncaring to reproduce the high-tech and precision made items of modern warfare. Doctrine was to build it simple, reliable and producible, investment was lacking in the underlying industrial capability, so stolen or invented the USSR just lost the ability to actually make things. They missed the switch from military hardware being the cutting edge to civilian and often consumer goods being the leader, without a robust consumer goods sector the Soviets were at a grave disadvantage in innovation and next generation technology. Sadly in terms of talent the Soviets had ample stock but the system all too often just wasn't able to tolerate innovation or translate it into product.