This stat alone tells you all you need to know. I honestly don't even need to post anything else. Marner has 67% 5on5 defensive zone starts in the series. He is playing the majority of 5on5 against Bergeron who is the best faceoff guy in the league and has been dominating this series in the dot overall. You do the math...
I have done the math. The effect of faceoffs at the large scale is rather minor. Given what we know about how quickly the effects of a faceoff dissipates and considering the faceoff percentage of Tavares, that equals out to a rather inconsequential advantage. A 67% dzs/ozs spread has a bigger effect, but based on the effect of the different shift types (DZ, NZ, OZ, OTF), what you describe amounts to a 2% shift in CF%, less in other measures. Now for the underlying metrics. That line boasts 45% in CF%, less in FF%, even less in SF%. That's abysmal.
Edit: I'm actually going to withdraw this point. Their xGF% is actually more than fine, and it's the best measurement. So let's strike the claim that they are on their heels, they are doing quite fine against the Bergeron line.
3) Solid point in your favor. However, that still means that in the rest of their playing time against other lines, they have been leaking. And that matters too, not just how they do against the Bergeron line. We can expect them to put up a fight and nothing more against Bergeron, but that line should own the Boston mid six. It's been the other way around.
4) We should table the discussion on Marner. He's not on topic here, and I don't want to spend the time bickering about how bad he's been.
Do you think they are 90 point players with 67% defensive zone starts playing ~75% of the time against Bergeron (4x Selke winner etc...) all year?
They are also not expected to be 90 point players in those minutes. They are expected to be better than 27 point and 14 point players. You exaggerate the effects of the contextual numbers as well.
Edit: You know, this is not fair either. Can't judge their even strength production in the series against all production in the regular season.
But hey, you've done a decent job of convincing me. I'd still say that you lean too much on contextual numbers and tend to ignore everything but the Bergeron matchup, but it's a solid case here. See what happens when you focus on your arguments rather than insulting people?