> Punch in December 2000 for start and today's date for end. You'll get 398% total return. 398/21 = 19% annual return.

I don't think you understand how percentages work. 19% annual return means on average every year you get 19% of the amount you have at the beginning of the year, not 19% of the amount when you began investing in December 2000.

If the 21-year return is 398%, the correct annualized return is pow(1+3.98,1/21)-1 which is 7.9%.