The current tags are incomplete, and route relations have become invalid when the railway key was changed.

If you only have "railway=disused", when you make a query, you have no way of knowing whether you are talking about tram, subway or railway tracks.  Other tags are missing.  This might please those who only see OSM as a day-to-day map for practical use.  But our map serves many purposes, such as being a reference map to create printed maps, to make accessibility studies or to compute statistics, e.g., the length of tram tracks in every city.
This is the reason why I reverted some edits from the new user who undiscussedly erased entire tram infrastructures in Brussels and in Antwerp.  Probably with good intentions, but with very short-sighted.

In general, it is better to keep public transport infrastructure unchanged during temporary closures.  But service changes that will last about one year are sometimes worth mapping, provided it is done in a coordinated manner, i.e., keep the route relations in sync with the available infrastructure.