It's curious that the same people that say that bullpens are volatile will point to prior year's BP record for the Yankees to suggest that they won't get much from further BP improvement.
In fact, the thesis of the fangraphs article occurs towards the end of it, and it doesn't quite support Quimby's point:
Sure, it feels like the Yankees won’t easily be able to improve relative to 2015, but that’s not the right comparison point — they’re improved, relative to what would’ve been expected. That’s what’s most critical. Chapman makes the Yankees better, compared to the Yankees without Chapman.
But here's probably the most important part of the article, especially as it pertains to the Jays:
"Here’s one way to see the effect of a great bullpen. We’ll go back to using those last 20 years. Teams with bullpen WPAs north of 10 have averaged 96.5 wins. Teams with bullpen WPAs between 9 – 10 have averaged 94.9 wins. Teams with bullpen WPAs between 8 – 9 have averaged 92.8 wins. Teams with bullpen WPAs between 7 – 8 have averaged 94.1 wins. Teams with bullpen WPAs between 6 – 7 have averaged 89.8 wins."
As you can see, bullpen seems to be pretty important. We really really really really need to significantly improve our bullpen.