You've missed the point: a climb to 500ft (arguably, before reaching 30 degrees pitch attitude) is not aerobatic.
Currently, we have no knowledge of what caused the accident. Pitch radius depends on power, speed, g loading, configuration, and air density ... adding 300ft (or any other margin) does not affect the pitch radius and therefore is not a guarantee of avoiding terra firma.
This accident was tragic, but accidents happen and can not be prevented by regulation, paperwork, or anything other than wrapping ourselves in cotton wool and doing nothing. Every human activity is a balance of risk against benefit. If we believe an activity brings benefit we can mitigate the risk by taking a range of actions and we can learn from experience. The investigation into this accident will result in a series of actions and recommendations to reduce the risk of a recurrence - it can not prevent a recurrence unless the actions are so severe that they stop flying displays.