I rebodied a P bass, with a PJ body yesterday, and it sounded totally gutless. Today I realised that the two 100k volume pots were 10K, so effectively 5K across the P pickup.
I've ordered a pair of 250K pots which should sort it. You could argue the ideal would be fitting two 500K pots, then the arrangement would be electrically identical to a P with the J pup wound right back.
I don't buy that the J-pup 'damps' the strings to any audible degree.