Let's face it. Rattler simply is too green right now for the hand he's being dealt. He's hesitating on decisions and he doesn't have time for that as he's running for his life behind a decimated offensive line.
I'm not expecting Haener to be some magical answer, nor at this point do I think he has more potential to be the future QB than Rattler does. However, I do think that with a year on Rattler, he has a better shot at producing points than Rattler does. He's got a year of NFL under him, watching and learning. He has a better idea how fast dbs and pass rushers are, and who is open enough to throw to and who isn't. He won't be perfect, he'll make mistakes as well, but he has a better grasp of the NFL right now than Rattler does.
I still think Rattler is the more talented and will be the more polished player in the long run but right now the more polished player is Haener, so he should start for now while Rattler continues to watch, learn, get a deeper knowledge of plays, and a better understanding of the difference between the college and professional speed of the game and the talent.
If the Saints just want Rattler to learn from the "school of hard knocks" and aren't worried about destroying his confidence behind that patchwork line, they can keep playing him, but I think it smarter for him in the long run to sit and watch for now.
Just my thoughts.