The money needs to be tracked from his last extension until this one, that's why they want the year statement to make sure the balances are within compliance.
While Vietnam doesn't really want to see 500k for 6 months, they do want to see account activity, to get an idea of your legitimate spending/income/financial habits. I'd have shown the idle 500k in the savings account, plus the activity in your daily account that hopefully has a substantial balance or continual topping up to account for spending or incoming income or what have you. You have provided zero details on your soft power activity, you haven't said what it was, who the provider was, how long the activity was, nor their success rate with DTV documentation.