Here’s my take on it . I have recently been asking myself the same question. Hence me riding them back to back and over the same terrain and mostly the same distance except a longer rode on the dual suss to see if it can handle the distance . We both know the stache & gravel can. Bearing in mind the ds is a 130/140 66* deg trail bike than isn’t very light , 13,7kg I think . Here’s my thoughts . If you can only have one bike the stache has to be it as the gravel grinder and the mnt bike . But,and a big but,if you dong mostly outrides and not bothered about bike park type rides then the gravel bike with wider bars can ride 80% of what the stache rides with no bother and a a damn site faster with a lot less effort. Yep the 3.0 tyres are boat anchors in comparison to a gravel bike and over distance. The fatigue is definitely tangible and to some degree. The stache vs the ds= The stache is more efficient and faster over flat dirt roads,not gravel fast but definitely faster than a ds. Going down the stache is quite capable as I am sure you are aware ,but compared to a 130 ds it’s obviously needs more attention to keep up the speed. Climbing up semi smooth ascents it’s close . But, add some rocks and corrugation or roots and undulations and the ds even at 130 seems more efficient to me . Less getting bucked out of the saddle,less paying attention to to line choice and generally easier. Time wise not much in it , but it’s the fatigue factor here that counts. You have to think less on a ds. If you had a 100/120 ds it could be the one bike to rule them all. Not the best at everything but very capable . I recently on a ride with a mate jumped on his yeti asr c and he had spin on the stache . It was immediately apparent how much less effort the yeti took to propel it forward . I was genuinely surprised at the difference. Over a 100 plus kilometres it would be huge for me personally. My ds vs the gravel bike is almost the same difference again if you can take the harsher ride. Over the yeti it’s still quicker and with less effort. For me personally I love my gravel bike more and more . Even though I know can do marathon type distances on my ds I am more and more leaning away from this bike and the type of riding it yearns for . Maybe it’s an age thing but enjoy my gravel bike more than any other bike. I think it’s the freedom thing combined with the speed you can hit on the dirt . Apologies for the waffle