I owned a Prophet 6 once, and have owned 2 OB-6 (probably my favourite modern synth). There's many posts on the internet about the distortion sounding 'better' on the OB-6, it may be more likely that while the distortion is exactly the same and in the same place it just sounds better being applied to a MUCH nicer sounding engine/VCOs/Filter and VCA section.
I was always underwhelmed by my Prophet 6 (I've since got a Prophet 10 rev 4.. now THAT sounds like a prophet!
) and, again, many others noticed how tame, small and distant it sounded for a VCO analog. The mixer section has no saturation and if you turn everything up to full it just sounds hard and sterile, while the OB-6 can push into the filter like a Moog does... now combine that more saturated texture and the nicer sounding oscilators with the distortion and, yeah, it seems to 'glue' to the sound better.
Furthermore, with some resonance on the OB-6 and just the right amount of distortion, I've created some of the greatest sounds to come from a single keyboard ever.. perfect for low drone intros and bridges... I never got that from the Prophet 6 as it just sounded harsh with the distortion (and not too great without sadly)