You are ignoring the benefit of deferring taxable income while you are in a higher tax bracket while working. If I was in the 39.6% bracket while working, and pay 22% withdrawing the retirement funds, I saved 17.6% over your method of paying 39.6% to invest that money in taxable and paying 0% when selling the fund. It's all about tax arbitrage.
Many companies matched at least some retirement savings contributions, a further benefits.
Also, if you have all your investments in taxable, you likely have a lot of dividends. That eats into your $80K space of 0% LTCGs. As a single, I have very little room for 0% LTCGs.
I never had to worry about the 39.6% tax bracket, I don't know that I ever got into more than the 15% bracket. So, I suspect it will work for lower income individuals, but not higher.