Hidan doesn't have immortality. He needs to fufill a quota of sacrifices to continue living. Oro wanted something entirely different. Sasori had more immortality then Hidan. Hidan>zetsu
I wouldn't say Hidan is the worst, it's just a matter of all of his attacks stem from Taijutsu and his Jashin ritual. I'd say realistically he's on par with Sasori. Sure as hell beats Zetsu, that's for sure.
Hidan is not immortal, he is invulnerable. He cannot be killed but he cannot live forever either. Sasori had immortality but not invulnerability. He would never age, but he could be killed. Just to clear it up.
Hidan is way better than Zetsu. Ok and I would even says he's better than sasori and ya kno what I say he can hold his own in a fight against Konan but he's is not the worst Zetsu is
Kishimoto wanted to give Hidan more tricks but didn't have the time to since he was pressured into introducing Sasuke quickly.
But heck I just made a thread about Hidan getting trolled and I can realize that he's on a lower tier than Sasori. Seriously the poor guy gets the "oh he's weak since he got beat by Sakura and an Old Lady" treatment and I can't help but sigh X_X