Where did I say that? Don't put words in my mouth. Of course the new engines are needed for more thrust, thrust vectoring, and stealthier nozzles.
I'm just pointing out that ur opinion is flawed. A lack of stealthy nozzles on the J20 isn't a big enough factor that would make it light up on radar. This is where u started off ur argument...
"And the J-20 can be defeated because the current version is not complete. It still requires a lot of work, especially a new engine."
So again u have been unable to provide solid proof backing up ur argument about how without those new engines the J20 can be defeated as if the rest of its stealth factors somehow don't matter.