I was unaware of landmarks, but I’m going to try it now that you mention it. I assume it can do alternative routes? Edit: Answer is Yes according to : A new "hybrid" mode: ALT = A* with landmarks
I didn’t check the demo route till now, but it actually takes the best route. Mine doesn’t for some reason.
On my server, best route is given as an alternative which is OK with me. The reason I can’t is that if I enable alternative routes, with distances over 50 miles and near cities, it takes so long that users think the app is broken. Thus I had to disable alternative. Now they cry the route isn’t ideal. I can’t win 
Either way it would be nice to provide alternative routes at a reasonable speed like 1-2 seconds for a 80 mile/128 kilometer route. Hopefully landmarks can do that.
“TERRIBLE” ALT ROUTE GIVEN WITH CH.DISABLE=FALSE
https://graphhopper.com/maps/?point=36.260134%2C-98.479582&point=36.144667%2C-98.934288&point=35.923393%2C-98.973427&point=35.754692%2C-98.772191&locale=en-US&vehicle=car&weighting=fastest&elevation=false&turn_costs=false&use_miles=false&layer=Omniscale