You are mistaken. Currently, the higher income you have here, the higher tax rate you have, where the highest tax rate on income sits at 47%, which you get hit by when your income is above 300K/year. People between 60K and 300K sits at 45%.
And then there are regional differences, someone in Andalucía don't pay the same amount of taxes as someone who lives in Catalunya for example, where the top tax rate is 50%.
Even taking into account other taxes we have, you still end up paying more in taxes the more you earn, unless you start engaging in schemes to lessen your tax burden, obviously. Although the social security is capped, so it does increase slower once you go beyond the cap, but it doesn't start regressing which your comment hinted at.
Edit: important to note that the tax rates are all marginal tax rates, maybe that was a bit unclear.
This is basically inviting your best and brightest to move to the US and other low tax countries.
The US is not a "low tax" country, it's just underdeveloped in social services. Which might give the impression the tax rate is low, but it's not - it's very high. Not only are you going to be paying income tax within 10% that of a western European nation, but you also have lots and lots of invisible taxes.
For example, did you know that about 30% of all compensation in the US goes just to providing health insurance and other benefits to employees? One of the downsides of having an underdeveloped health sector is that it's quite expensive.
Or, how about the fact that the average American spends 15% of their gross income just on transportation cost? Turns out having all that underdeveloped transit infrastructure isn't free. We pay for that.