The question is not what percentage they pay of income, that has no bearing what so ever on how much they can reduce their price with the elimination of the tax. You need to compare the amount of tax with their gross sales to how much Wal-Mart could reduce their prices. Your analysis is meaningless.
If you pay over a third of your income in taxes, the elimination of those taxes would have no effect on the price you have to charge to still receive the same after-tax income?
Oh, but it (the %) does have a bearing since tax costs cascade (which are calculated based upon profit) and become embedded into the prices of everything we buy.
These "hidden taxes" exist and are a real - but non-productive - increase in prices that we all pay in everything we buy. The analysis was right on.