I'm not sure it's a case of "getting it wrong," though.
I mean, read Paul. (E.g., Romans 7.) For him all the other rules from God are just essentially a trap, something nobody can uphold in its entirety, so everyone deserves death. (NB, I don't think Paul has our idea of Hell. For him it's either you earn eternal life, or you're still dead.) The whole point of the Law for him is just to make that clear. Whether you're the most devout Rabbi who's ever lived, or literally Hitler, EVERYONE deserves death in Paul's interpretation.
So, yes, only Jesus can forgive you, because otherwise no matter what you've actually done, you're just as much of a villain as Ted Bundy in the first place. It's not a case of yeah, but now you can go be a villain. It's more like, you ARE a villain in the first place anyway. At worst, you can go on and continue to be one. Or you can ask Jesus for a pardon.
Also, whether Paul himself was a gnostic or not, it does sorta align with the whole gnostic/initiation-cult views. For those you are trapped in this world, and only the secret knowledge can offer a way out. It doesn't matter whether you're a villain or not, it just matters whether you can get out or not.
Hell, for some not only will obeying the rules not save you, but obeying the rules is what is trapping you in this crappy lower universe in the first place. E.g., take the Cainites. These guys literally revered the first murderer. Literally, the biblical guy who invented murder was their hero, not villain. Because again, for them obeying the rules of the lower demiurge who created this world is what traps you here. Actually going out and doing some murder, theft, adultery and a good bit of coveting the neighbour's ass, is how you might save yourself. Though the secret knowledge is still the better bet.
TL;DR: actually it's intentional, rather than "getting it wrong."