I think others have complained that this forum, despite the views of its members, have veered into Fanboy territory. I stick to my heterodox views relative to this forum; the J-20 is too clunky to be a truly breakout Chinese fighter, whatever others may think (ventral fins, canards etc in a stealth configuration, both not deadly, but unwanted)..
As for the IPE / WS-10X engine, it's possible that the IPE / WS-10X is mainly a reliability improvement on the J-20. The Chinese have made breakthroughs with rhenium blades recently, and a main contest between Western and Chinese/Russian engines has been a question of lifespan and durability. The Chinese have been intensifying training of late, meaning that Western-style fighter engines with high service life is more necessary. On the other hand, the WS-15 could be heavily overclocked to reach 170-180kN, and the WS-15 might not be able to sustain the same lifespans as reliability-improved WS-10. We do know, however, that the WS-15 seems to be a low temperature engine (good for IR stealth), so that the WS-15 might also have service life improvements.