I'm not mistaking "rebuilding" for "tanking." I come from a family of contractors, carpeteners and construction workers. Remodeling one room in a house is not a rebuild to me. Moving on from the QB is not a rebuild to me. Like I said it's a subjective term that means different things to different people.
You're assuming Rattler would be the starter. Carr leaving doesn't necessarily mean Rattler would be the starter.
Which is why I don't think they will cut Carr and not bring in someone else. Moore and Loomis made it clear that they want to compete. You don't get the college record for most wins as a QB without an obsessive competitive streak.