Sure, one can revert everything in bulk but I won’t do this, because this will create another giant bounding box, which would annoy every mapper.

Instead, I reviewed them one by one and looked for interesting tags that could be kept, before removing duplicate information.  The only one I left untouched was the viewpoint here: https://www.openstreetmap.org/node/100337302 It looks okay.

The rest has been fixed.