Hello. Firstly, hats off for a superb site and very useful routing engine. We used it in France very successfully over a 500 km touring trip between Auvergne and Périgord finishing in Agen.
However on a few occasions, the routing engine seemed to choose a route on small roads (which we normally much prefer) but with a number of very steep hills (+140m) , over a (longer + 1 km over 6.4 km)) route with on what appeared on OSM as a major road. The computed time seemed to take only distance into consideration. The longer route was only downhill and obviously that extra km would have been quicker than the additional 140m of elevation. But the main issue was the steepness of the hills. A real pain.
So the request is really to have a routing rule that could take into consideration the steepness of the route and also not ruling out major roads totally when they make sens and it's not long.
I understand this is in reality a complex request, but thought I'd share it anyway.
I think the lesson here is to use tools for what they are and agree, as users, to spend some time to study routes a bit better, using the fantastic tools you provide. In my case, a bit more time spent would have allowed me to spt what we were up to and I could have made the decision myself.