I don't want to start another "OHJ" thread especially as it is not relevant to this accident, but the issue with the OHJ should be readily apparent:
- multiple planes can arrive concurrently, with the possibility of a mid-air because they are all at the same height and it is geometrically infeasible to guarantee that each can see all the others
- while everybody who has arrived is going round and round in the OHJ, they again can't see each other so separation assumes looking ahead of you and hoping that a) you can see everybody ahead and b) they can see you.
It is really a very dodgy system. Something like a crosswind join is much safer because you are approaching the airfield from an area in which there should not be other traffic (except another plane also joining crosswind, but he should be able to report his distance to run and not lie about that as many do) and you have the whole airfield and the circuit nicely laid out in front of you. Also you will normally be descending so your visibility is even better.
People who like the OHJ are probably the same people who think a lookout is perfect, but there is ample evidence that it isn't.