Here is what I found, and what I believe some possibilities could be based on that.
I started off by considering the biggest shift in the team this year was Thornton going down, and that might have affected many players, Tierney included.
So I parsed the data for before and after Thornton.
Before at ES-
Pts/60 1.36
G/60 .68
CF% 52.43
FF% 53.04
GF% 52.38
SV% 93.03
ZS% 56.66
PP pts/60 7.29
After at ES-
Pts/60 1.85
G/60 .62
CF% 45.61
FF% 47.35
GF% 44.64
SV% 89.12
ZS% 44.37
PP pts/60 2.99
Now a couple things stand out here, in my opinion.
One, Tierney actually scored more pts in the back half of the year. So his production was not the issue.
Two, his possession stats took a nose dive. Was that Tierney starting to fade, or different line mates on his line because of the major Thornton shift making that happen. Ill get to that in a sec.
Three, he went from getting very offensive zone starts, to getting very defensive zone starts. This could easily be a partial cause for the much lesser possession numbers in itself. Also the save percentage dropped through the floor, not sure if that was because Tierney, or whomever his linemates were, player far worse defensively, or he was getting bad luck on the ice.
Lastly, in the first half of the year, he was absolutely killing it on the PP. He and Labanc were number one and two, in pts/60, on the team, not just the 2nd unit. Considering before Thornton got hurt, Labanc was primarily on the 2nd unit with Tierney, it seems our 2nd pp suffered greatly for it went Thornton went down. I will say this too, Tierney was still the highest pts/60 player on the 2nd unit in the latter half of the year. So his numbers were hurt from losing Labanc as a PP partner, but he still showed, IMO, that he was the best player still on the 2nd unit as far as the PP goes.
Ok, so getting back to line mates for Tierney, and if something shifted dramatically after Thornton went down.
I went and manually checked a sampling of games from before, and after, Thornton got hurt. To see who Tierney was starting each game with. Obviously line changes could occur in game, but it IMO, still gives at least a semi decent idea who he was with for the most part.
Before the injury, Tierney played mostly with some combination of Boedker(mostly), Donskoi, Karlsson or Hansen. In two games he played with ONE of Meier or Labanc.
After the injury, the first couple games he was still with a mix of those players above, minus Labanc. However for atleast the last 20+ games every single game he was with Meier and Labanc at the same time, of the games I looked at.
I think it might be fair to say that as a line, those three don't mesh. More specifically I think its Tierney and Labanc who don't mesh, just a hunch, because they are both more playmaker than shooter, both small and relatively easy to knock of the puck. Labanc is not particularly defensively responsible yet, and when we also consider Tierney's ZS% dropped dramatically, at the same time he is playing primarily with Labanc and Meier, it might further indicate why possession stats, Gf% and SV% took a nose dive for Tierney in the latter half of the year.
Also, that line was the worst in the playoffs for us at ES, IMO, which further solidifies my belief that those three should not be a line.
What's you opinion, based on what you see here, or have found out yourself.