I don't understand why you are mentioning the lanes must be equal since we can change line? Why is this important in digital?
In analog racing, it's customary for the drivers to rotate through all the lanes. For that kind of racing, length doesn't matter much for the actual racing, because everyone gets a chance on the short lane(s) and the long lane(s). Equal lap times are nice for close racing, but the actual race is over many heats where drivers get a turn on each lane.
For digital racing, it's rare for there to be any kind of rotation, since, as you said, they can change lanes. The race is usually a longer race, often with fuel/pit lane activity along with the actual racing. When the drivers in a race are not equally/closely skilled with closely matched cars, the lane length really doesn't matter. In fact, many people never get into a race where that's the case, and so never experience the frustration of a track where the lanes are uneven enough to make a pass extremely difficult. Why would it be difficult? Well, imagine two closely matched cars/drivers. They both naturally gravitate to the lane that gets them around the track faster. In the majority of cases, in my personal experience racing on a wide variety of tracks, the faster lane is the shorter lane when they are unequal. So, whoever gets into that lane first in the lead, is much more easily able to hold onto the lead, because the only way to get ahead of them is to change into the longer, slower lane, and push extra hard to get ahead, hoping that the other car makes a mistake or otherwise does not keep pace and falls behind. Usually, it ends up coming down to hoping that the leader makes some kind of error and falls behind.
But, when the lanes are of equal length, it's more likely that they can be traveled in a similar amount of time. While there might be a preferred lane, the other lane is not nearly as detrimental, and a driver has a much higher chance of getting ahead with some skillful driving, even if the other car does not make any egregious errors in his driving.
Again, though, this really only matters when there is real competition, and not so much when it's just for fun with a bunch of people that are not matched well. The faster cars go around the slower ones until the race ends. I also know that many people will eventually settle on a layout and not want to change it. If you make the layout above, and end up with some real competition, you will find this situation to be frustrating, but changing the track might be prohibitive for some reason.
That is why I always encourage people to move toward a layout that has equal lane lengths if possible. If they don't want a bridge/overpass, that's fine, but the LAST thing you want to do is make a bridge that creates an even greater difference between the inside and outside lane lengths. I've raced competitively on tracks like that, and there really is very little hope of making a pass unless the lead car(s) crash.
