What a bummer.
I'm really curious about how the conclusion was reached the only solution to correct this problem was to replace the entire subthrottle assembly. Could you elaborate please?
Not knowing anything else it seems way more likely to be a sensor or wiring issue and way less than a $1500 fix. In the service manual every mention of subthrottle problems indicates an open or short in the wiring or fault in the subthrottle sensor.
2018 Ninja w/bags, Motowerks lowered pegs, Sargent Seat, Puig/Vstream screen, Givi XS307 tank bag, WOLO BadBoy horn, Aerostitch Roadcrafter