@Dacon62 exactly. @JackQ these engines and their controls are much more complicated than that. Under perfect conditions on a dyno I'm sure you can get similar numbers with different types of gas. But we don't run our boats in those conditions. Intake air temp, oil age and viscosity, coolant temp (especially on a lake with seaweed that clogs filters) and even fuel (your 87 vs my 87 vs the 87 they used in this demo) are not all created equal.
These engines run a 12.5:1 compression ration. Why did GM run ratios between 8 and 9:1 for 50 years and only switch to 12.5:1 now? Were they just stupid for all that time if you clearly can run 87 in a 12.5:1 engine without issue? We know 12.5:1 is better because it is more efficient, makes more power, and burns cleaner.
The reason they didn't do it and the reason they require high octane in vehicles with this engine is knock:
Gm has smart controls engineers and they know not everyone will put high octane in their trucks all the time, or that people make mistakes, or even that sometimes the octane rating at the gas station is incorrect. So they design the system to retard the timing in the case of knock to keep from damaging the engine. This lets you run 87 and maybe you won't notice, especially driving to get groceries in your truck.
But it's a different story in a boat. We push the engines way harder than your average truck owner. We load the engine to the max coming out of the hole during the deep water start, run at high rpm and power down the lake for ~30 seconds, then drop on the ends and the engine heat soaks for a minute before we do it over again and again. This is not what these engines were ever designed for. Unless you are pulling tricks or wakeboarders you will get knock doing this with low octane fuel at some point. When that happens the ECU goes into a derate mode to protect the engine and then the power curve shifts. The Zero Off settings were dialed in for these boats using good fuel and with the engines running properly. As soon as the power curve shifts the feel of the boat shifts considerably.
Maybe if we could go in and adjust the gains and other variables in the ZO software we could make it feel the same running 87, but currently that's not an option. And even if it were, you're still potentially damaging your engine long term, which is why GM says not to use less than 91.