Both are wuxia with mystery and awesome action. Both have good CGI. ML rise from young age to become powerful cultivators, starting from being extremely weak. Cultivation school life also covered a bit like BTTH, ML is a prodigy in school. Both have powerful and kind masters. Good master-student relationship. Both ML are righteous and upholds the ideals, they both have precious secrets about them. Both have a big revenge to take . Strong and beautiful female leads too.
Sword dynasty also has good romance. In all, it is nice to watch.
The main reason I recommend this is that both dramas are good wuxia and the have some shared themes. the overall arc of the male leads are similar in my opinion. if you are looking for another good wuxia, then look no further.
Both have romantic relationship between an older women and a younger man. In ROTCH it is a master/apprentice relationships, The relationships in sword dynasty has a similar dynamic, male lead calls female aunt, its the same in ROTCH. When I was watching ROTCH I kept thinking of sword dynasty.
In both stories the protagonist trains to increase his spiritual power in order to take revenge on people who wrongeded him in the past. Having to hide their teal identity, they have to overcome many difficulties including some kind of sickness or curse in order to achive their goal. Supported by the female lead they make friends who will support them on their quest.