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"
Not only metallurgy is important but the forging technique as well. Design is also very important.