You're missing the point. Neither of them should be seeing that many throws when the first string QB wasn't even seeing that. The offense is broken and starting yet another QB won't change that. It just disrupts the offense another time for no reason. Rattler completed 71.4% of his passes last night despite the high number of throws, which is still higher than 3 of Carr's games.
You made the very point of asking, "Who really wants to see Haener to come out and throw 37 passes?" I answered that I think Haener is capable of handling that volume and gave back up to support it.