1) 20/20 hindsight is a wonderful thing
2) You can't foresee every eventuality
It is. And, of course you can't. But it's 20:20 hindsight, examined with the proper respect given to those who didn't have the benefit of it, that allows us to learn and improve the way we do things. And that makes it even more important not to use hindsight to attribute blame.
If we don't examine the evidence we have and re-evaluate the procedures after accidents like this, we're not doing a good job of managing safety. That doesn't mean that things have to change every time there's an accident, but it's right to consider the questions raised, and I don't think your dismissal of the relevance of the issue of student solo is warranted.