That's true but for any strong shinobi, he's easy to beat either way. And for fodder shinobi, aka
the majority of NV, then his ritual is unnecessary since he outcombats them anyways. If you really
think about it, any time he used the ritual in combat, he could've won without it anyways so it makes no difference.
Hidan would only be OP if partnered with someone else OP. For example, if he chilled far away while Madara
fought Hashirama, and then Madara ran from the fight and brought a blood sample with him, then Hidan can kill Hashirama for
Madara like that. But as a fighter himself, his ritual is useless, just his good taijutsu and kenjutsu + immortality
that helps him along.