it's both. A bit like the bafang BBS.
i can hit 15mph with a little effort on assist level 1.
That's why I can't see the point of haing 18 selections while 3-9 would do.
It is like having 27-speed on your e-bike.
Are you talking about the Oxygen system? If so you should have a go on one before commenting on it from some theoretical point of view without understanding how it works. There's two separate controls. one is for power and the other is for speed and an associated power profile. You wouldn't normally adjust the power on an ad hoc basis, but it gives you a chance to adjust the overall power to match your needs. A light rider or a medium rider with fairly flat rides might choose power level 1, then use the six speed/power controls to adjust the power and speed as the ride demands. A heavy rider or someone with a lot of difficult hills would most likely choose power level 3.
Having extra options is always useful when you want to use them. There's nothing to compel anybody to use them, but in this case, there's no penalty for having them. it's purely optional what power or speed you want to use, when you want, how you want. Why would anyone not want the choice?