All the above implies the routing is able to assess the route about correctly, based on available OSM data. E.g. and just illustratively, it takes 3 min/km for one part on an easy road and 20 min/km for other part on a steep woody trail.
I repeat my comment about the extremalities. You do not really expect the planner would consider the muddiness, unless there is tag surface=mud. If you do not evaluate in advance yourself the ETA in extreme conditions would not match, is it yours fault when they do not match and you are surprised.
You would also use different profile configuration for short sportive rides and long trips or expeditions.
Thinking is required. ETA calculation is not magic, it is simple calculation, that can be easily fooled. If one does not count with it, it is his fault.
I repeat my comment about the extremalities. You do not really expect the planner would consider the muddiness, unless there is tag surface=mud. If you do not evaluate in advance yourself the ETA in extreme conditions would not match, is it yours fault when they do not match and you are surprised.
You would also use different profile configuration for short sportive rides and long trips or expeditions.
Thinking is required. ETA calculation is not magic, it is simple calculation, that can be easily fooled. If one does not count with it, it is his fault.