Maybe a good idea for the director to physically see the whole display to assess its safety before authorising it?
A good start for sure. There may be a bit more to it than that, though if the "Director" is experienced with aerobatics, they will know that a loop is very dynamic maneuver, and it's success or failure is pretty well set by how the pilot handles the exit from the inverted position in the loop. Get that wrong on the way down, and you're going to consume much more altitude than planned - so that allowance should be built in to the program.
Somewhere, I recall discussion about a hard floor at 500 feet for that show. Though appropriate to a much smaller aerobatic aircraft, I imagine (not being a jet pilot) that is a demanding target for a high inertia jet.
On the whole, I would hope that airshow organizers balance safety with the need (or not) to see aerobatics performed by vintage or high inertia aircraft. We're lucky to have these vintage aircraft flightworthy and displayable at all, do we need to wrap them around on top of that? My vote is just to fly them by a few times.....