I just doublechecked your samples in the linked thread, both contain gravel roads, I guess this leads to the long ETA. However, when throwing them as gpx into Calimoto I receive this result (due to import deviation longer distances then in Kurviger, but even there no suiting ETA):
While downcalculating to the real distance of your samples with an average factor we have an ETA in Calimoto for the first route of 4:23 h and 6:20 h for the second one. This significantly deviates from your statement:
Would you mind to explain? Or did I make a mistake?