It used to bother me too, until John started singing along with Outkast.
I think he might be deliberately adding exaggerated affectation to sound more like his brothers, to overcome his upbringing.
I also think it's Aaron's Pierre's acting choices for his American accent
I am trying so hard to take the Lanterns plot seriously, but the way John Stewart pronounces "ASK" as "AKS" in literally every single episode has completely broken my brain lmao. It doesn't matter how intense or serious the scene is, the moment he says it, my mind completely clocks out of the mystery and I can't think about anything else for the next ten minutes. Please tell me someone else is noticing this.