I dont expect him to be a top pairing defenseman but it has happened under 2 different coaches in multiple years where he is just awful for stretches. Earlier this year there was an obvious stretch that he was the worst d-man on the ice. Petry was great the year the habs traded for him and started out well the following year and then nothing but peaks and valleys ever since. There are high peaks and low valleys and Petry hits them all.
I honestly don't see it that way. I find him fairly even, and he has his tougher games every once in a while. Don't know what valleys you're referring to. It's not any more probing than it would be with any other player.
As for his peaks, they often seem to coincide with increased responsibility. He's a great PPQB, but we only get to appreciate him to his full extent in that role when Weber is out of the line-up. Him doing well on the 1st PP wave goes a long way into making him look good in a general sense, hence the appearance of a peak . That's my theory, anyway. I've really liked Petry's game on this team since day 1. He has tougher nights, but so does everyone else.