It's been studied over and over. Lower taxes mean more economic activity, and less tax evasion.
An article in Spanish
https://www.elindependiente.com/economia/2021/04/25/madrid-d...
Another one
https://www.libremercado.com/2021-08-03/el-efecto-laffer-de-...
En concreto, la región de Díaz Ayuso recibió de la caja común apenas el 23% de lo que ingresó en 2019.
Meaning that Madrid out of the 100% taxes it collects for the State, only 23% end up in Madrid. But that's still fine, because of the higher economic activity.
Madrid has been accused of "tax dumping", by having way lower taxes than other regions, and still:
Tanto es así, que Madrid aporta en torno al 68% del sistema de solidaridad interterritorial (más de 4.000 millones) frente al 25,5% de Cataluña o el 6,6% de Baleares.
Meaning that, even with low taxes, Madrid funds 68% (+4 billion Euro) of the inter-region fund system.
https://en.wikipedia.org/wiki/Laffer_curve
