Almost sounds like TC is kicking in, unless your talking about the on-off throttle that has been like since the 2013 zx6r 636 as with other bikes, it is to do with emissions and the fuel decel cut.
The false neutrals are a worry, however i had similar issues with my 2016 ZX-6R 636 when new till first oil change. Only false neutrals i get now is when I am to soft on the gear lever when using quickshifter at full throttle.
After the ECU flash that on off throttle was gone.
Cost/price wise and such I cannot comment.
It a shame you have had a bad experience with your bike, I do hope you do get a decent price when sold.
2016 - Kawasaki - ZX-6R 636 (ABS)
Rear Wheel 130HP / ~97kw & 53ft-Ib / ~71nm
Mods: Two Brothers S1R Slip-on Exhaust, Decored OEM headers, LED lighting conversion (Headlights, Markers, Indicators), TST Industries Taillight light and TST Industries Fender Eliminator
Woolich Racing ECU Tune w/ Race Tools: Quickshifter, Launch Control & Pit Limiter
Planned Mods: Braided Brake Lines
2016 - Kawasaki - Z125 Pro
Mods: Yoshimura RS-2 Exhaust, Airbox delete with Short Ram Intake with Pod filter and LED Headlight and Markers Conversion