Wei Ying tendency to not stick to the trifles =/= disobedience.
Under Jiang FengMian’s governance, Jiang Sect might look very much like it has no rules because Wei Ying is so used to drinking, playing with kites, hunting pheasants on top of his studies and practices. But, it’s not like that. Even when Jiang Sect’s teaching isn’t carved in a stone wall like Lan Sect, it always has one, that is to “know what’s the right thing to do even when the situation is unforgiving for such action” (I believe in English version it’s translated to ‘attempt the impossible’), and that is one crucial teaching that Wei Ying always obeys despite being lenient with the trifles. The teaching wasn’t written out, but it’s already carved deeply in his heart.
For Wei Ying, it’s not that he does not follow rules, but it’s just that he has his own rules to follow; something that’s built upon his own belief, experiences, moral compass, and principle.