I don't think that's fair. Calling Beirne a fine player is an understatement, and while he might be "unproven at this level", he can't prove himself at international level without being picked. Meanwhile, he's arguably been the best player in European club competition for the last two years with the Scarlets and is still on top form now. He was one of the stand out performers in the Italy match and scored two tries.
He's done literally everything he could have done to get picked. He's played well and has made no errors. He's massively unlucky to not be in the 23.
That's not to say that it's ridiculous that he hasn't been selected, as we have good depth in the second row right now and no current injuries. In the end, Schmidt is just showing faith in the guys he usually picks, which is consistent with Marmion being picked as the starting 9. There's nothing wrong with that. But equally, if he had picked Beirne, I don't think there could have been too many complaints. In my mind, he's a better all round player than Toner and on better form than Henderson at least. If I was picking the team, he probably would have been on the bench for the All Blacks game. I think he could be pushing for the starting 15 come the World Cup, along with Ryan, but for this game it makes sense to give Toner a start to steady the lineout.