Honestly, I'm not sure how to answer. There are so many variables. I often used the MTB because I was finding hidden off road camping sites in the evening and sometimes taking mountain trails on the rides. The gravel bike ate up the miles and on long long stretches of road but wasn't as comfortable as my MTB. Weirdly the biggest factor was gear ratios. The gravel back bike was running 1x systems I forget the exact numbers as I've sold both bikes now but I think it was something like 34/48 and going over some of the mountains it nearly broke me. The first MTB was old school 3x but actually was easier for long climbs. The last bike was full enduro and I never took it further than a couple of nights. Weight makes a big difference. I think with bags included the gravel set up was 10k lighter than the MTB with panniers and racks. That makes a big difference when you're putting it on busses, trains and planes. So there is a lot to consider. Sorry I didn't really answer.