I thought the heavier and longer the bullet, the faster the rifling twist has to be to stabilize it...
This is correct. I think it's the profile of the wadcutters that does it, they're just not very aerodynamic. Not usually a problem because not a lot of people shoot to even 50 yds with pistol rounds. Lyman did actually upgrade this design (the 429/180WC) to be more aerodynamic by adding a pointy nose, while keeping the full caliber sharp shoulder, now a 200 gr boolit. That one is prolly no good for a lever action though, being pointed.