Nah, that's just what the jealous China-haters tend to claim
It is a Chinese designed fighter, with international technology from several manufacturers - like practically any fighter design of these days.
I may have overstated when I said it was "a Lavi" since it is not a 100 percent copy (it is bigger and was redesigned when mission roles were shifted). But, I think you are understating the degree of core influence the Lavi data and that reverse engineered F-16 supplied by the Pakistan provided. What percentage of the underlying technology was generated in house? About the same as the Chinese PL-9 missile? It’s not identical to the Python 3 either, different control surfaces even…but it's still an AIM-9L+ capability missile.
The J-10 certainly seems to be a significant technological departure from preceding "indigenous" aircraft like the J-8, which showcase 1970 Soviet era technology. From SU-15 era to F-16 era, I’m sure with only the slightest influence from Lavi research and a reverse engineered F-16. Then there is the contemporary J-11, which is just a licensed-produced SU-27, showing no real indigenous effort.
Of course, the real victims of the J-10 may be Dassault and Saab and the Eurofighter consortium (F-16/18 exports too) since the J-10 is seen as being a major export item. Pakistan has shown an interest in replacing its F-16As with the J-10. Enough of the capability -- half the price!
It would be a lot easier to dismiss if we actually had an armada of our next generation super planes. But we don't, and won't have for quite some time. And if a conflict occurs we won't be fighting in a controlled and advantageous environment like we had with Gulf War 1 or 2, where we were on the offensive from secured bases fairly close to the action against a military at least a generation behind (technologically) where China is heading. The don't have to be able to beat us in some "Red Dawn" scenario, they just have to be capable enough to control the region for a limited period of time.
Charon