Are you honestly saying that using a step-function is what makes taxes so complicated?
There are two parts that make taxes complex. The first is deductions. That takes up a bit of the complexity. The second is defining income. That's hugely complex.
In one easy to identify problem, your system seems to imply that I have to pay taxes on the value of any asset I sell, not just the appreciation of that asset since purchase. Which makes investing... interesting.