I think those of us who own one do not feel as though it really lacks anything. It sounds like a typical PJ bass to me. The biggest weirdness is the PJ arrangement on a Jazz body, but if you like the idea of a P-bass with a Jazz neck then here is one ready-made that way without any mods. I also believe a large segment of the TB community that do NOT like the JP-90 feel that way on account of the oddly shaped pickguard that vaguely resembles a bass clef symbol.
These basses were only made for about 3 years, 1990-1993 if memory serves. The earlier ones did not have a skunk stripe on the back of the neck while the later ones did. The later ones with the skunk stripe appear to be more prone to neck problems than the earlier ones without the stripe but not all necks with skunk stripes are necessarily bad.
JP-90's have a Poplar wood body instead of Alder or Ash, and this makes them lighter than other Fender P's. If you are a "Wood Matters" kinda guy then the Poplar body could be an issue. Personally, being an old geezer, I like the lighter weight.
Typically, the JP-90 is the most inexpensive MIA Fender P that you can buy on the used market. If you like yours then there is really nothing to carp about.
There is a JP-90 club where you can see what owners like and dislike about their axes. I suggest you check it out to more fully educate yourself. I think these are great axes, especially for the price:
Fender JP 90 club?