Not only metallurgy is important but the forging technique as well. Design is also very important.You know the capabilities of Tejas better than any Chinese or Pakistanis.
Second i met a Pratt and Whitney design engineer in Canada and guess what he said every engine is pretty much an improvement of the last one. No company tries to re-invent the wheel.
As long as the Chinese get the metallurgy right all is well, even if it's just "a copy"