I have always attributed the difference in aura on that rooftop scene between Wong and Adam to be due to their situation. Adam had lost everything, and was totally defeated, deflated and in a hopeless position, and his overall posture reflected that. After his little discussion with Damian, Adam's back straightened just a little, his face calmed down just a little, and he regained his composure and coolness. Wong, on the other hand, had this aura of righteousness and arrogance about him, which completely suited the situation he was in. Both men were not meeting on even terms, and hence they could not possibly generate the same aura.
There was also that earlier scene with the fake Adam, of course, and even then the aura wasn't quite the same. But hey, it wasn't supposed to be the real Ye Gucheng, was it?
Nevertheless, despite being an Adam fan, I have to admit that as good as an actor he was, Wong Yuen Sun completely nailed the personality of the lonely swordsman and you just couldn't compare the two performances - in the same way that Wong could never play Chu Liuxiang the same way Adam did.