All teams slump, lines & groups of players slump at different times on both good teams and bad teams; I don't think we should kid our self that we are an ok 5v5 team, lots of teams look statistically better if you can remove one inconvenient stretch.
If it was a uniquely peculiar set of circumstances like both your starting and back-up goalie got injured and you're forced to throw some AHL kid in the deep end, I mean sure put an asterik on the GF% for that stretch, but we were healthy and just played poorly, it's part of who this team is and likewise for the good stretches.
The point is to provide context for advanced statistics. If a team wins 5 games in a row with a 1 goal margin and then loses 1 game 8-1 what would you say that team is, considering we using GF% as a measure? Bad? I mean it could be bad, but you'd definitely need to provide me with a lot more information to strengthen your argument and for me to have confidence in what you are saying.
If I would be in the business of using just convenient stats I could have just said that we have great stats in more than half of the games we have played (obviously looking at the ones we've won). That would be using convenient stats. On the other hand if you are looking at a sample size as small as we are right now and don't include context as I just did in the previous post then I would probably argue that it is you that are using convenient stats, probably because it fits your narrative.
The bottom 6 was basically completely new going into this season and we had a new coach. I know that there were several posters which at the start of the season questioned the narrative that the bottom six were useless, and that they wouldn't not provide any kind of secondary offense for the full season. At the same time players like McDavid and Draisaitl are not as dependent on system play and/or coaching to be effective and they came out flying. McDavid was on ice for 17 GF and 7 GA (71 GF%) in October, while the rest of the team was on ice for 8 GF and 18 GA (31 GF%). Those are crazy numbers, and to an outside observer obviously outliers. Looking at the rest of the season, i.e. the following 42 games played the GF% numbers are even between McDavid and the rest. If one quarter of your dataset off-sets the results to that extent I would consider it essential to provide this kind of context, not to do so would be disingenuous.
The second part basically follows the same logic. There were many theories about why we were losing but in the end it does not matter, what matter again is the context of the numbers you are using. I didn't go down to game by game basis, I went for month by month. It is possible to break it down further by looking (conveniently) at Dec 4 - Dec 27, 12 games with the team at 31% GF%. The rest of the season, i.e. 46 games, 50% GF%. Again, that is very important context if you want to understand the numbers and essential context if you want to draw conclusions from the data.
For me this kind of goes towards the downside of advanced stats, many people don't realise how much a bad stretch of games can influence the results. At the minimum I think this needs to be pointed out when using these numbers.