So then, what is the point of stropping on Denim?
Just paste paper, cardboard or craft foam, if you want a flat substrate.
Many of us have test stropped, the same razor daily on paste, for well over a year with no ill effects, to the razor or edge.
It is not the substrate or the paste that damaged the edge, it is technique. Convexing a bevel is a good thing and will not affect the edge, other than to strengthen it.