He's a top 4 defenseman on a team that won back-to-back Stanley Cups. I'd say it is a safe assumption he would have become a top 4 defenseman on this blueline, especially if you view Matt Roy as a top 4 dman. Cernak is considerably better than him, hence his newly signed 8-year extension.
I disagree, it is easy to say anyone is a god on a team that stacked as it covers for a lot. Their third liners are all going to earn $6M/year now...
I don't think he is bad, he is a good defender, but he is the weakest of the four, and had he stayed in LA, I don't think he would have developed and been utilized as a top 4 defenseman of the same status. I think he would maybe be #4 but would likely be in the group mixing around between 5-7 if he were still here at all is my assertion. I think that is more of a slight to LA than Cernak honestly but is just how I see it.
With Cernak, I don't see a very good stay-at-home defenseman or puck-mover/point-producer, even on a team as stacked as the Lightning. I see a decent rounded defenseman who isn't particularly specialized that can slot 4-6 on a few teams but needs a good partner. He had the luxury of being glued to Sergachev which is awesome, but since being there he hasn't played over 67 games or put up more than 18 points, and while he isn't soft or mistake-prone, I don't see him as being particularly hard to play against.
In the end, he is a good defenseman, I just don't see an amazing top 4 talent that was lost and feel that if he had stayed in LA he wouldn't be close to the position or status he enjoys now, so good for him, but I am not too broken up about the loss even though it was a pretty clear mistake by Dean to let him go for literally his own piece of mind for a few weeks.
