I too would finish it. It’ll turn out to be quite a surprise and a learning curve in the end you watch.. bet something else decent comes along that will be a referral from it.. you watch.
We’ve all been there, honestly I’ve long since lost count of the Programmes I’ve been on that involve some bloody awful badly run work stream that the PM has walked away from, damn if I hate them for it too.. I never refer any work back to them after their walkout either, sod em’. If they approach me first instance and say “I’m in da shit, need some help/resource/SME” then I’ll assist and support and thing better of them for it.. and the world turns around once again.
Walk away, stay away is my mantra.
There is nothing that can not be done, even the shittiest Projects have some glaring amusement about them. I never say “knuckle down, MTFU” because I believe in assistance, sharing and support and drive.
It will turn out well, you watch.
HTH’s
All IME.