Pretty sure Haener has the same amount of up side that rattler has. The perceived difference is all hearsay at this point. The actual difference is just hype right now.
Rattler has an elite arm that Haener does not have. That's what I mean by more upside. Haener has a fine arm but Rattler can make throws that Haener and most other QBs can't make. But that doesn't mean he is going to be a better QB.