GOING BACK TO THE WIKI TO FIND EXAMPLES OF WUYANG’S PERSONALITY IN CONNECTION TO THIS
One of Wuyang’s respawns has him saying: "As Anran would say, I still have a ways to go. "
Which she does indeed say (lvl 67 [lol] on Anran so I've heard it many times).
Anran here is telling herself in a healthy way that: she can always improve... though... it has an underlying issue. The pressure shes under to be better than perfect.
Wuyang also faced that pressure to be like his sister, to be "perfect." He only just managed to escape being a complete disappointment by his parents thanks to be becoming a great healer at Wuxing.
Now, Wuyang doesn't have any lines like Anran does where he puts himself or others down (at least not harshly, hes just cocky), in fact, ITS ACTUALLYTHE OPPOSITE:
"Wow, you're incredible!"
"Oh! Yeah, I'll accept compliments for that."
"Ah, you've got nothing on my sister."
"Whoops! Got a little ahead of myself there."
Bonus I'd like to add since its a rare voiceline and cute interaction when Anran gets a kill:
Overall, his voicelines make him seem confident in himself, though as we know, he wasn't always like that. In "Elemental Kin," he clearly states he feels like Overwatch picked wrong. And Anran at the start and end, when he proves himself to be capable, emotionally tells him he is worth everything hes done up to that point. He has always felt the pressure to improve thanks to her always hounding him (as well as his parents through Anran), and when he finally sees she always believed in him, he gets that ego boost telling him that he is indeed worth it.
But Anran doesn't get that...
Sure Wuyang says shes great, her classmates, teammates, friends, teachers... they all say shes great. But do her parents feel that way? No. Not at all. At least not outwardly. They're "never happy" as stated in an interaction between the siblings.
Anran never gets to be told by the people who push her so harshly that she's great. They only continue to put her down, and in turn, thats all she knows. Put others down. Be harsh. They can only improve like that.
Wuyang had that space to grow, make mistakes, and be great at what he does with support. Anran was neglected and was pushed to her limit over and over again. She spared him as much pain as possible, and while its clear Wuyang was intimidated by Anran, he always held love for her, and she held love for him. They had each others backs always, despite her harshness. He likley saw growing up all that she had been through. He saw how she blamed herself for his shortcomings, his mistakes. And he saw his parents emotionally abuse her. So he stuck by her side trying to influence her that she too is great. And while it sometimes shines through the cracks on rare occasions, its usually back to her being aggressive.
Anran is both perpetuating and trying to break the cycle her parents passed down onto her. Most fear her and hide, while those like her brother, and other unknown students saw that there was more to her.
Shes trying hard to push up instead of tear down, but for a long time, its all she knew.