Yes, wideband is critical to optimise mixtures. It is NOT used by ECU to adjust mixtures. But data is analysed by a human who goes in and re-programs ECU for more powerful settings than factory's good-enough compromised settings (for MPG & emissions goals).
Factory ECU under partial throttle uses O2 sensor for feedback and will use data to adjust mixtures to 14:7:1 AFR for best emissions and MPG. This is known as closed loop-operation.
Under WOT, ECU ignores narrowband flip-flop O2 sensor because it can only detect 14.7:1 AFR (open loop operation). Instead, ECU just looks up fixed pre-programmed map using LOADxRPM reference points. These maps are optimised for safe and reliable operations, typically in 11.0-12.0:1 AFR. Carbs are even worse with super-rich 10.0-11.0:1 under WOT.
This is rich setting with extra fuel for safety in case you get bad petrol from station out in boonies, or run WOT on super hot day. Or have failing fuel-pump or clogged injectors. These conditions can cause lean fuel mixtures and result in detonation/pinging, overheating, and blown headgaskets or holes in pistons.
But rich safe mixtures robs lots of HP since max-power is obtained around 13.5:1 AFR (remember that '60 hot-rod saying?). So... the wideband O2-sensor gives you AFR data under WOT open-loop operation so you can optimise mixtures away from factory too-rich settings to more powerful 13.5:1 by re-programming ECU maps.
On Ninja 250FI leaning out WOT mixttures gives a substantial +14% increase in power! Note how inconsistent factory WOT fuel-curve is, it's wavy and all over the place. Adjusting it to most-powerful flat 13.5:1 curve picks up torque & power all across powerband.
