sure but here's what happens in practice. The agency raises the revenue, and raises the spending to meet the new revenue.

I'll give an example. My local city proposed creating a separate taxing authority for the fire department . The new authority would get an additional share of the property tax. Meanwhile the city would keep the share they were getting beforehand, and spend it on other things.

My point is that abstract / theoretical approaches to taxing don't account for the human factor. The human factor is that people just want to make their job easy, and if they get more money, they will spend it.