The tax change is not to corporate tax rates. They stay the same. It’s to individual taxes, and as such would only apply to small businesses run by an individual who files as an individual. A very small number of small businesses run in this fashion generate over 250K of profits – and of those that do, most don’t generate that much more (given the incremental nature of tax brackets, it would mean a 4% hike in the top tax bracket would translate to less than a 1% increase in total tax burden for any individual making under around 350-400K).