They are that
The property taxes here aren't just for schools. Instead the state government has been tapping into them for other purposes such as medicaid. Of course that means that they are higher than they have to be for their intended purpose.
That's highly unusual since most areas now receive state aid, or use other taxes to make up for the shortfall in funding because property taxes no longer cover the full cost of education.
This is what the NY City lawsuit was about. Like the fact that small population states have a disproportionate influence in Congress due to the fact the Senate gives two Senators regardless of population, NY State also gives disproportionate influence to lightly populated upstate NY. So the state funding for education gave these areas more money for education than they did for NY City. This violated the state constitution.
The real problem with upstate NY's tax base is the area is overpopulated. This is because from the time America was created until about the end of WW2 western NY was an important geographical location with its access to the Great Lakes and shipping.
Once the interstate highway system was built, and growth happened in other parts of the US, western NY was no longer an important hub. Cities like Buffalo and Rochester withered and major manufacturers like GE moved out of the area. Also, Kodak.
Western NY is not suitable for large scale agriculture, and without the advantages of being a shipping hub, and without the excess electricity as the Niagra Falls hydropower was exceeded, Western NY found itself with too many people for its economic importance. Yet, the population did not move away in sufficient numbers. Hence its economy is not great enough for its people.