There are a couple of things that I've heard that are consistent with this
Out of phase. Really, really sensitive to motion/touch of the sting, all top end and attack, can be grating sounding and brash
Near-broken connection. You can get it if some wires are just hanging on by a thread or if components (switches and pots) are knackered. Bassless, much less hot, tinny, cold, quiet, all attack, no note.
'Semi-short' if you will; a short thats making light contact, so it kinda doesnt totally short out.
Disconnected pickup, as in at the source, in the pickup. That is very unlikely, but I've had it with one pair of trilogies (something about new solder I seem to recall) a few years ago, and soldered the wire from the wind onto the wire proper again and it sorted it. (I've seen one USA fender where the wind wire and wiring wire were glued in place with solder applied....nowhere near each other!)
And at the extreme, a pickup will still make a sound thats not inconsistent with what you describe if its connected at live or ground, but not the other. Theres still a small signal.
The wiring looks neat with good soldering, so nothings obvious, and I dont know that switch off the top of my head, so I cant say if its all rightly wired, but the rest is fine, and the switch wiring looks about right so I would look to the other components, change them one at a time. If that doesnt work, I'd just touch a soldering iron to the contacts on the bottom of the pickup so it liquifies, and see if that works.