Is his personality and charisma really THAT bad? I don’t think it’s as terrible as people are making it out to be.
I mean he’s no Rock or Austin but those are diamonds in the rough.
I don't think anyone is trying to compare him with Austin or Rock, just like people don't generally compare the scorers of today with Gretzky and Lemieux. Even in an era where promo ability and charisma are largely lacking he is no Bryan, Joe, Nakamura, Owens, Lesnar (not for promos but charisma and presence) Woods, Lynch, Asuka, Ambrose, even Cena (who I can't stand). He's basically a guy who is quite good in ring and in great shape and is athletic, likes goofy outfits and bad monikers, and not much else. Doesn't cut promos well, even considering that WWE gives them crap, and doesn't provide any real subtle aspects of character either.
In wrestler terms he's still relatively young so you never know though. Bret Hart picked up steam massively when he was older than Rollins is, Eddie Guerrero first showed signs of a personality in the LWO when he was around Rollins' current age. Even if he never shows much in that regard he could maybe end up as a Benoit or Styles, but he needs to get a bit better in ring for that.