I don't mean to come off as harsh, but your reasons are wrong. Piketty isn't some random guy who threw together some numbers and came up with a theory. His work is extensively researched and reviewed. He's thought of and responded to every objection you made. If you are interested in the topic then you should definitely read his book.

Take a look at your numbers again. You have made multiple mistakes. Your 8.4% annualized rate is wrong - You can't just take the start and end points to calculate an average. Plus, you are plugging quarterly data into yearly calculations.