I did some experimenting after your post, and I noticed a small, but probably significant, difference between the settings. As has been stated here, these settings are about bandWIDTH! Obviously, the bandwidth inside of the 2.4 radio spectrum (can we call these channels?) is different at differing frequencies within that spectrum, right?
For whatever reason, as you pointed out, Autel decided to have it always default to 10MHz. This might be similar to DJIs strategy of always hopping around and searching for the strongest signal. It makes sense, but OTOH, I think the user ought to be able to decide and then not have things reset automatically.
All that said, I looked closely at the graphic when switching "channels" and noticed that the "band" is indeed narrower at lower channels. This implies of course that less information can be carried at lower channels, because the "width" of the band is smaller. In other words, less width = less ability to carry more signal.
And yes, a lower frequency does go further generally. The earlier generations of drones and RC models usually carried video at the 5.8 MHz frequency. While the video was better, the penetration was less and the signal didn't carry as far. I think most modern drones are standardizing on the 2.4 band now. Of course, that cause problems in itself, because the 2.4 band is very crowded and that is where WiFi signals are carried, so if you are in an area where 2.4 is ubiquitous, then you stand a bigger chance of having interference problems. Frequency hopping methods like DJI and Autel use are their answer. For me, I have decided to amplify my signal and enlarge my antennas. I think this might cut through it all and give me enhanced video and control.