I wouldn't personally consider Kanjuro to be betraying Luffy personally, Luffy didn't pick him or interact with him for more than a few sentences, he wasn't swept up in Luffy's wave of charisma at all, he was someone vetted by Kin'emon. In other words Luffy hasn't messed up in his recruitment of allies, his allies have, so I don't think it makes sense to be a big learning moment for him.
Luffy didn't seem to be mad or affected much when Kanjuro's nature was revealed after the initial one page of shock, it's not like he really bothered to hunt him down or mention him since.
I know what you are trying to say here, but you wouldn’t get these specific requirements and based on those you can say something counts as a treason or not.
what I’m trying to say here is that we have seen nothing special from Yamato that makes someone wanna trust her, someone might argue Yamato one shot Ulti, one of Kaido’s Tobi Roppo ... but that’s not enough proof since Kanjuro fought alongside the SH Too but he still betrayed everyone eventually.
i’m not saying this is a mega problem that Oda absolutely ruined everything with, it’s just how I think Why most people feel Oda did Yamato’s character injustice (till now) by not exploring her background and make some actual characte development that makes us discuss her with complete Understanding of everything about her.
what’s happening now is basically Yamato character being introduced as a good character who joined up with the Main good character of the story to take down the bad character.
I expected more than this, that’s all what I’m saying.