In other developed nations, taxations are one of the things that drive the economy of the country further but they out in place many things to actually make it work out.
You don't understand much about it. In developed economies, taxes screw up economic growth. A minimum level of public services is necessary, and for that, a minimum level of taxes is acceptable, but the state is tremendously inefficient as a market player.
If you don't want to talk nonsense, you could say that in advanced countries taxes are used to redistribute wealth to the most disadvantaged, which is only partially, and minimally, true.
Regarding this 20% flat tax proposal, I would like to see it in those countries that my friend is talking about here, which have much higher income tax bands. But no, here it looks like a measure that aims to increase the revenue currently collected by the state, which is detrimental to economic growth.