I've had both Prophet 6 and OB-6 (still got the OB-6 as it's 10 x better sound wise to me!), also had the Rev 2 which has similar/same knobs as P6.
P6 knobs were fine but due to the size they felt a bit picky, and turning them wasn't as fun or smooth as the OB-6. On these DSI pots you could (on p6/rev2) sometimes feel the imperfections as they turned, kinda like grit, there was no damping. On OB-6 there is space between the part you touch and the pot shaft so you don't perceive that gritty feel which is a great bonus on the OB-6 when you are working with its glorious sound, the controls feel as good as it sounds.
OB-6 has wider caps (all the same pots underneath no doubt) but because they are bigger caps they FEEL more solid to me. well the plastic itself doesn't feel 'solid', and the metal tipped/rubber knobs on the P6 did feel nice, but in action the OB-6 feels 'better'. Smoother, more assured, more fun and smoother as the radius is bigger so you can turn it slower as you change say the cutoff.
Neither of mine, nor rev2 had 'wobbly pots' or wonky pots, all good, but rev2 and p6 felt more similar to me I guess than OB-6. Ob-6 is better by maybe 10%? feel and use wise? nd even looks wise in reality it's a non issue as I feel I reach out for them better (due to a better control panel layout on OB-6) so it's more intuitive and they just feel nicer in the fingers with space around them)
It's a chunkier, more robust feel on the OB-6, while P6 feels a bit idiosyncratic and 'small', not sure if the spacing is different between the pots to allow for the larger caps but if so that would also explain why the layout feels more fun to use and I can grab knobs better without double checking like I had to on the P6/Rev 2.
None of them are bad, but when you factor in the OB-6 sounds 10x better in most cases than the P6 (to me) it's a no brainer to prefer the OB-6.