That is a very inaccurate assumption and one based on stereotypes. The avionics and the subsystems of the J-20 has already been completed by 2009 and was in incremental improvements program ever since. Unlike Russia, China has the luxury of multiple corporations and the competition between them to generate a high quality supply chain. The Chinese also have far more experience and has produced far more models of fifth generation avionics than Russia has. Note how, for example, China has deployed AESA radars on the KJ-2000, KJ-200, KJ-500, ZDK03, J-15, J-16, J-11B, J-10B, and Z-8AEW, ever since 2003, while Russia has not even had a single AESA radar in successful service. The same goes for weapons. The Chinese have already tested their fifth generation engine in 2009 and rumors claim that another one will be done in 2014.
J-20 is not a bomber.