I don't know where this idea came from about Avgas being for low compression, low rpm, but its common. It may come from some confusion on the different rating methods and labelling. In the US, octane for road gas is the average of the motor octane and the research octane tests. Whereas octane for Avgas is given as lean mixture and rich mixture tests.
But comparison is relatively straight forward. The first or only number on Avgas is the lean mixture octane. Shell states "
Avgas is measured on Lean Mixture (similar to MON)" and the second number represents octane tested under rich mixture conditions.
So 100/130 as well as 100LL are roughly comparible to a road gas with MON of 100. In other words, 100LL has a MON roughly comparible to a race fuel with 100 MON.
Interestingly, there's a new grade of 94UL Avgas being tried out. It's supposed to be based on the 100LL but with no TEL and has a Lean mixture or Motor Octane of 94. This is intended for lower compression aircraft that used to run lower octane Avgas that now is difficult or impossible to obtain.
In fact 100LL is required for high compression and supercharged aviation engines, whereas a lower octane fuel is all that the majority of prop planes need. But a lot of companies like Shell aren't making the other grades anymore.
https://www.shell.com/business-customers/aviation/aviation-fuel/avgas.htmlhttps://flycorvair.net/2015/08/26/compression-ratios-fuels-and-power-output/https://en.wikipedia.org/wiki/Avgas#100LL
