My criteria is to split the ways so that we can have a clear mapping of the (staggered) pedestrian crossings. This doesn't happen regularly so I am not too concerned about scalability, though with continuing urbanization, we will find more and more of this "single -> double" case from irl-upgrading signaled crossings.

With me starting to know how JOSM works, I can start fixing my past mistakes, but ultimately I gotta know why the quoted two relations are broken, and how they are broken, which naturally leads to how to fix them.