Your math ain't mathing.
And the logic ain't logicking because we already have prototypes set up in this country to assess how it works and if it's effective. People aren't going to buy groceries and sneakers out of someone's trunk to save sales tax that they're saving in eliminated income tax, unless they already shop that way.
The overlords don't want it simplified. They want a behemoth federal government Gordian knot so We the People won't look too close at it. Not that we'd look at it anyway because when push came to shove we couldn't even agree that government needs to stop spending so much freaking money on bullshit.