The second discussion, and this is where I disagree with what you have said, is about whether he's a good playoff goalie or not. I tend to think too much is made of how players perform in the playoffs vs regular season, but if we're going to judge his playoff performance in isolation, we have an 11 game sample to work with. There are too many random variables to draw significant conclusions on 11 games.
If the team stays as they are, then at what point do you hold the goaltender accountable? On one end, Allen could post a .920 and stand on his head and the team loses. On another account, he could post .880 behind a horrible defense. At what point or place would we agree on that he is accountable?
This is also 2 different discussions though. You can hold a player accountable for a single bad game or shift. You just can't draw broad conclusions from the small sample size. It cuts the opposite way too obviously. There's a difference between, "He needs to be better in the playoffs," and "he's not a good playoff goalie." You didn't explicitly say the latter, but it seemed to be implied.
I probably worded it poorly and I do apologize. What I'm trying to ask is, at what point is the team's success/failure due to Allen and what point is it the team in front of him?
I don't know of an exact way to answer that. If you lose 1-0, it's on the offense. If you lose 7-0, it's on both. If you lose 7-6, it's on the goalie. Those are all obvious though.
In that series, it was both. I'm not going to hang a series on a goalie when the team scored 2 goals or less in 4 of the games. But, in those same 4 games, Allen allowed 4,3,4,4. That's not amazing either. There's so many variables at play though. I think it's fair to say that the team lost that series because everybody was subpar, both skaters and goalie alike.
Big picture, I don't think anybody can look at his 2.29 GAA (which is legitimately good) and say that he's a great playoff goalie. I also don't think somebody can look at the series we lost against the Wild and say that he can't hack it in the playoffs. I'm optimistic with him, but I don't think anybody can point to his playoff performance and say anything meaningful in either direction. There's just not enough evidence.