I mean Warner had success in the Martz system which was vastly different than the Shanhan/Kubiak system. A major part of that is the QB has much less control and much less ability to change things up than in the Martz system. So, it's not surprising at all that Warner doesn't like it.
But I do think that the play calling for Rattler in the Chargers game was overly conservative and they didn't really set him up for success. The play calling for Haener dramatically changed and opened up. But maybe that's because Rattler wasn't ready for that stuff?
But, if Rattler wasn't ready for that stuff then why did they start him over Haener?