I don't know if we can use Qin Yu and Xiao Hei as the norm for the Xiuyaoist way though. He has probably the most powerful technique and cultivation methods ever created, the Meteor Tear (which is still really unknown what it can do, or what it has been doing besides healing), and top grade holy weapons with unprecedented external methods even before Stellar Transformations. He really is a freak accident so his improvement rate will be incredibly fast.
Xiao Hei is also a bit strange in that he is some crossbreed with heritage memories that give him abilities even the supposed king of eagles [golden flame] doesn't possess. His ability to use and refine jindans is also probably many times superior than normal Xiaoyaoist methods.
That said, it makes sense that practicing as well as stealing jindans would be stronger than just practicing
.