What makes me saddest is that Jia ruined Yongcheng. He could have been so great. And even he was smart enough to know that his mother's scheming was going to get them into serious trouble. But for Yongcheng, it was either obey and get screwed or disobey and be called "unfilial"
That is true, what I do believe that if he had gone about it the correct way, he could have avoided a lot of the fallout. He should have confided in Ruyi. She most likely would have found a way to have him assigned as her foster son and his honesty would have overshadowed him not being filial as he is supposed to be a good subject. Hell, him being honest to protect his mother from an even worse punishment could be seen as filial.