“If Powder stayed and heard Vi's words, there wouldn't be a misunderstanding ”,
except there would still be one.
Lets see, we have the scene here.
"She made a mistake", "She's young"
Vi is only excusing Powder's inexperience, she's in her sister's side. Still, if you think like Powder, It still would feel like she doesn't truly trust you.
"You know what, Mylo? You are right. There's a bunch of thing that Powder just can't do [...] Like complain about everything, and brag non-stop, [...] Take fights with the group when we need to focus [...] And tell strangers on the street that we got a nice call"
All the "good things" Vi says about Powder actually only are a (very direct) indirect way to call on Mylo's flaws.
"Powder's my problem, Okay? Your problem is you never know when to shut up"
Even in defending Powder, she still takes responsabillity of her actions. She's note saying she's capable or a good item for the group; only that she answers for Powder's mistakes.
So, does It change so much the scene if Powder heard the rest of the conversation? Not really.
Powder's mental health was already compromised, and even if she knew her sister had her back, it wouldn't wash away her feeling of guilt. Hell, maybe she would try even harder to prove Vi she's not a liability, that she's not her sister's problem and she's as capable as Vi at her age.
Actually, my "biggest complain" about that scene is that, had Powder stayed a little more, the writers could have used the "I'm still your problem, right sis?" Or something similar after their reunion. Maybe not even say something to Vi, but when she talks about her with Silco she would say "I thought she believed in me, but she considered me her problem"
Ah, maybe It's a little bit too corny?
Anyways, the "leaving the scene before hearing the twist" trope fits the moment, but in the greater scheme of the series It didn't change significally the plot. I totally can see people only recognizing the trope and feeling frustranted by it; very understandable.
