Just because it’s not possible to separately buy the structure or the land doesn’t mean the numbers are wrong. The point still stands that taxing land disincentivizes nothing while taxing structures discourages building them. Many towns in Pennsylvania had a pretty good track record with this. They implemented a mixed tax system that focused more taxes on land and less on structures because they wanted to make people sitting on empty land and not using it pay more. They also didn’t want to penalize people for upgrading their home. The system was extremely successful in its aims.