A commercial flight flying from A to B and a military operation to do military training (with an installed Martin Baker let down option ) are completely different. As is an aerobatic aircraft doing a display overhead the airfield. Best we compare apples with apples.
If you don’t want a hard line drawn at 30 minutes, what number do you want??? If the rest of the world seems happy with 30, why are you so different??? What makes Australia so unique that we can’t comply with ICAO??
Yes the rules are written quite abruptly, if that’s the problem then complain about that and not the actual outcome of the law. Strict liability offences can still be defended, weather is an obvious one, higher levels not available due traffic will probably get you off too. Failure to plan properly will most likely not cut it....
If you can’t demonstrate to yourself or an inspector your ability to successfully complete a flight plan and allowing for a fixed reserve of 30 minutes ... best you don’t go flying that day!