Welcome aboard Poots! You sure pick a hot topic to post on. There are hundreds of posts all over the forum on this subject. I can scream from the heavens on the experiences I have had w/ different fuels, and fact finders can shout even louder.
Your points on what an engine is designed to run on are valid. However... The topic of degradation of both fuel, and engine play an important role. Climate/fuel handling, and storage/variances in engine tolerances (when NEW) all play a role as well as many other factors. Too much for a scooter rider to even care about. My firm rule of thumb is buy the best fuel the station offers, and if that is not good enough start blending your own w/ Avation fuel/C12/racing fuel. The ONLY scoots/engines that will require custom blends are out of the every day users realm anyway. It is strictly for those that know how fuel interacts/burns. Burn rate is the only concern as that is what creates power. Some engines respond to a faster burn rate, ie: lower octane, and others self destruct due to low octane. It all depends on the environment or conditions involved in the end use.
Cheap gas is like a cheap escort. I don't bother with either.
How do you like me now!