Yes because we all know that laws with millions of words are easier to implement and cost the government less to do so just like the most complicated doodads and gadgets are the best and least expensive way to do simple things as well
No one ever implied that, but simpler doesn't equal better which is a major selling point of you flat tax morons.
The major selling point is that it is fair.
Even though a dollar is worth a dollar, Dollars earned don't hold the same value all along the earning scale.
Look at it like this, imagine you're homeless and someone gives you a dollar. What is the first thing you do with that dollar? Buy food, maybe medicine, shelter or clothing. The basic life essentials. This is where mostly anyone would put their very first dollars towards. It's why you don't see homeless people saying "Will work for yachts". Those are items purchased with dollars further down the need scale. The first dollars anyone earns will be spent on basic life necessities.
This is why a progressive system that taxes these first dollars less and more heavily as the dollar has less value to basic life needs makes sense and doesn't put the poorest among us at a disadvantage. Is it perfect? No, but it's better than a mindless flat tax system that isn't fair to anyone but the richest among us.