Of course they are. 7 states in the union operate just fine without income tax including Washington, Texas, Florida, and Tennessee. People are net migrating to states without income tax. Income tax brackets are an excessive complication that are completely unnecessary for running government. You can simply make essentials like groceries and tuition tax free, and keep everything else a flat %. It works fine.

And if you need evidence to see that this statement is true, look at states where there is no income tax. It isn't just blue skies in those states. But you might need to look into the details to see that more clearly. There's no free lunch