Interesting observation. Did you compare low band (6m?) with high band (2m?) with all things being equal on this trip and still have better distance? Were you using commercial grade radios or amateur gear? Flat or hilly country? Open or forested?
In my not-so-scientific mobile comparisons over the years, low band (6m) seems to suffer more compared to 2m due to the higher noise floor and physical ground plane limitations, even with a near-quarter wave long (49") antenna placed in the center of the car roof.
To some extent 6 and 2, but more information is garnered from low band radio to high band radios, of which we (company) have both, as well as UHF itinerant. There is no difference from low band to high band be it commercial or ham. It's not like the radio on 6 meters is better than the low band. As long as the radios are designed to open squelch at relatively the same signal level, and the antennas used are the same type, then same is generally same. The only issue at times is propagation, and to some extent noise which is prevalent in on 6 as is LB at the same physical location. That said, there are some locations where noise can not be overcome on either segment. However, the only places which we have had noise plague us is metro city areas, or in a fully packed truck stop, or factory where welding and processing takes place.
A lot of our comms fall into two lists. On site coordination, and long distance deployment and logistics. Think of the coordination as being where the the truck with supplies is within several miles of the site, and you call the site to ask where to offload. Logistics is somewhat the same way, but at times it's hooking up with others on the road who are coming from other directions and want to all come in together. Deployment is where one is in a group on the highway were you may, or may not be traveling close together. This is the one area where any thought of a UHF Baofeng in the cab can be ruled out. A high power Retrivis VHF helps, but still is not helpful, not to mention a PIA to operate when driving.
The locations are normally rural, and noise free. In the city I may get S8 of noise on 51 MHz at a steel plant. Out at a job site, S1. Same applies to LB commercial. The locations can be a Saskatchewan or North Dakota prairie, or we can be deep inside a Tennessee woods, or up in northern Michigan among dense pine trees.
So to be fair, the bands can not be compared without the assumption that the antenna for the radio is outside, roof or fender mounted, and is unity gain or better on both 6 and LB, or 2 and HB. I've gotten a pretty good read on LB simply because my truck runs both a stainless whip, and Hustler resonator, for example for ops on 29.750 MHz and 29.600, both in FM mode. Same with 6m and 2m. After a decade of use, you get used to the performance of each. And no, I don't mind pulling into a rest stop to make an antenna change.
But back to the LB point, LB has never failed in the woods. UHF is worthless if you can't see (visually) more than 50 yds due to trees. HB is better, but LB makes the trek. LB is also fantastic on the prairie as flat terrain can give us the most distance, and thus sometimes as much as an hour's heads up to arrivals.
The key to comparison is same antenna architecture, gains, mounting, and power. And if the radios are similar in their sensitivity and selectivity, then it's fair. A lot of times in discussions, those factors get clouded as the transmission path is not equal.
In our mounting, heavy trucks have mirror mounts. Light trucks/pickup have fender mount LB, and roof VHF/UHF. Cars, only one car has LB but it's the same as the light truck in performance. Cars usually have trunk/fender mounting with nothing on the roof.