Personally, I agree with those who think PK2 is not really better than PK3 - just different. PK2 does have more detail in the highs and tighter bass, but PK3s sound more fun IMO. PK2 sounds kinda unnatural to my ears - the trebles are too prominent and the lack of deep bass extension is really noticeable. For some reason, I never really felt that PK3 lacked bass extension as much, probably because PK3s had more mid bass and it and so lack of low bass doesn't seem as bad.
BTW, I also noticed that PK3s benefit from a fast, neutral/slightly bright amp with good detail, like MiniBox E+ for example. It makes PK3 more detailed in the treble and more controlled in the bass. PK2, on the other hand, doesn't benefit form an amp at all, and may even sound worse with some amps.