Sorry I find this to be a very simplistic and weak argument.
1> Pardy and Ellerby's role, skill level and pay grade make them bottom pair guys. That is the role they play. I feel like most criticism of these guys happen when they end up on the ice against the other teams best players or are on the ice with the Jets bottom 6 forwards. Byfuglien is paid very well to be a top 4 defenceman so he should of course be held to a higher standard.
2> Putting all of that aside, my issue again with Byfuglien is, and always has been, the way he approaches the position and his compete level in his zone. As a defenceman myself I pay very particular attention to the defence when I watch games. I always have and I actually credit that in making me a better hockey player. My issues with Byfuglien are not based at all on stats. I know how dicey plus minus is and you won't see me use it to support an argument. What bothers me about Byfuglien is the fact that he loses his man in coverage, he is not aggressive enough with the opposition in front of our net. I also do not like the cavalier way he treats the opposition in our zone. PMo preaches doing everything 'fast'. Part of that is defencemen closing in quickly on opposing forwards when they have the puck in our zone along the boards and in the corners. Byfuglien does not attack the puck carrier nearly hard enough 80% of the time.
3> That leads me to what bothers me the most about Byfuglien. He shows when he 'cares' or is motivated he can do all of these things at a very high level. Problem is, I only see motivated Buff for fits and starts. I am afraid that is all you will ever see from him. He's a guy who could have been one of the best of this era but his lack of passion is stopping him.
He reminds me of the guys at drop in hockey who line up at D not because he wants to play D, but because he can stay on the ice longer and he can carry the puck and create offense with less backcheck pressure. Buff is still doing a decent job of getting points at forward but he is not as dynamic because anyone who plays D but has taken some shifts at forward can tell you, the pressure you face as a forward is far greater than when you are playing D. You get more of a free pass in the neutral zone as a D man with the puck, and you can sneak into spots and be forgotten in the offensive zone more often.
I might be old school, but defencemen should always be able to play D first and foremost. Creating offense is just what makes a D man special.