It absolutely is not, it's a parasitic relationship. Enough suburbs are aware of this dynamic that their local leadership tries really hard to annex their suburb into the city so that suburbanites can vote to change policies in the urban area. Suburbs strong arming cities into annexation is a common theme in the US and Canada.

How is it symbiotic? The developed, urban areas generate enough revenue to subsidize suburbs. Without those urban zones suburbs cannot generate enough revenue to provide the infrastructure and services they use.

If the suburbs were to be re-zoned for more dense development and mix-use zoning I don't think the urban areas would see any drop in revenue. They would probably see an increase.