My great fat ducky lumps of muscovy drakes get up and down my back steps just fine [they are 14-15lbs] My regular sized pekins [7-8lbs] are very agile up and down the back steps.
Ducks are not good on ramps at all The slope needs to be low and the ramp wide and smooth to have any chance of ducks using it.
In contrast ducks are good at hopping up steps and may fly down steps [even pekins can fly downhill from a top step!]