1. I agree with Wikipedia's proposed definition of "building". That makes wind turbines *not* buildings, merely structures. (There is no roof, they are not meant as a shelter, they don't even allow comfortably working in.)

2. Using outlines to specify the extent of a larger object is simply better (more detailed) information than just having a node with data slapped on it with tags. That should be obvious for even larger objects like landuse=retail (we don't just map the center of it).

3. As for the wiki page, it was *silently* changed in revision https://wiki.openstreetmap.org/w/index.php?title=Tag:generator:source%3Dwind&oldid=1867625 (22 June 2019) to not allow areas. Upon review, the change message is absolute crap, it gives no justficiation (direct or link to an external page) why generators no longer should be marked as areas. (and for that alone, I will see to revert that change)
osm-carto even still renders generator ways, and carto would be subjectively the first project to remove something if that something ought not to exist.