vtm VS le-bon-tag

You are correct, Valhalla is used for routing. Maps are rendered on the ELEMNT, BOLT and ROAM with mapsforge, BOLT2 with vtm. To look at map files there is cruiser cruiser (mapsforge) and cruiser-gl (vtm). Create updated maps with wahooMapsCreator. There is also some documentation how to add POI's or make a custom theme.

for an example. It's perfectly smooth. The application is closed source but the underlying renderer (VTM) is LGPL3. The renderer, https://github.com/mapsforge/vtm, is basically an OpenGL alternative for the mapsforge offline maps format and maintained by the same guy (the original mapsforge renderer is arguably a bit slow, struggling to hide its slowness behind cached tile bitmaps).

I've once spoken to an OSM "evangelist" and he really struggled to get this point.

In a way I got his point the OSM model can virtually store anything so it's the data provider burden to develop a glue code to interact with OSM.

However because of potential vandalism or sheer goofiness objects and ids can potentially break at anytime so writing glue code is actually not trivial.

Maybe a half way solution would be to promote generic glue code framework. I've heard about this project by a french local authority that help sync back data from OSM to your own database. Dunno if other similar projects exists.

https://gitlab.com/Geonov/le-bon-tag