If you want to rationalize it, age wise this is probably his peak. Early 30’s, been studying the dark side for ten years. By the OT, he was in his 40’s and been on a respirator for 20 years. He still whooped mortals’ asses in Rogue One and mostly beat Luke’s ass.
Didn’t Disney say they are already using an AI version of JEJ’s voice in this series? I don’t think he recorded anything new.
Plot hole (?): if she was going to foolishly attack Vader one-on-one, why now and not literally any time before now? Kenobi offered a tag team which would have been her best bet, but she turned it down and then attempted a foolish play. She might as well have just started putting bombs in his crapper dome thing where he hangs out while on his star destroyer.
Will her next play be to try to steal Luke to give her another chance to kill Vader (now or later on)…even though she just passed on Kenobi’s offer to team up? Or go full dark side and try to steal Luke to win back Vader’s favor? There’s no way she tells Vader or that an Inquisitor finds out about Luke, because Vader wouldn’t have let that shit sit around for 9 years (and not think it’s a coincidence when Leia drops the droids with Death Star plans off on Tatooine). I’m afraid this story is about to make even less sense…and every scene/interaction young Leia has with Ben makes her behavior in Episode 4 (and not telling Luke about it before ESB or ROTJ) very bizarre.