If you want to get a better idea of Lowry's performance at evens and where he deserves to be on the roster, we can look at GAR, since it combines his low scoring with things he does much better. It adds the defensive side, along with tilting the ice, and adjusts for usage.
Keep in mind, there are 90 first line positions. So, rankings of 1-90 (1st), 91-180 (2nd), and 181-270 (3rd) are what you should keep in mind.
Lowry's Ice Time
Lowry ranked 63rd in the NHL for total ice time for all forwards.
Lowry ranked 96th in the NHL for total EV ice time for all forwards.
In part due to being healthy for all 82 games and in part due to Maurice liking Lowry, Lowry got a LOT of ice.
Lowry's Impact
Lowry ranked 96th in Overall GAR.
Lowry ranked 129th in EV GAR.
This suggests Lowry gave the positive impact of a 2nd line forward.
Breaking it down into it's individual components, we can see how Lowry drives wins:
Lowry ranked 181st in EV Offense (mostly due to his positive impact on linemates as his scoring is weak)
Lowry ranked 22nd in EV Defense
Lowry ranked 62nd in PP Offense
Lowry ranked 273rd in Penalty Draw
Lowry ranked 96th in Penalty Take
Lowry ranked 22nd in Face Off Win Value
The issue is that Lowry generally got more ice time than his performance suggested for evens. Being 96th in overall impact with 63rd in ice time is not great. Being 129th in EV impact is not as great when you are 96th in EV ice time.
Lowry's Impact Relative to Ice Time
Lowry ranked 123rd in Overall Impact per Minute
Lowry ranked 143rd in Even Strength Impact per Minute
For components:
Lowry ranked 246th in EV Offense per min
Lowry ranked 79th in EV Defense per min
Lowry ranked 99th in PP Offense per min
Lowry ranked 310th in Penalty Draw per min
Lowry ranked 289th in Penalty Take per min
Lowry ranked 49th in Face Off Impact per min
Take Home
1) Lowry drives offensive and scores like a fourth line player
2) His defensive impact makes him a lot better than a fourth line player
3) He probably should be on the 2nd PP unit rather than the 1st
If you are looking at pure impact, Lowry could be passable as a 2nd line forward...
That said, I don't like specialized defensive players on the top two lines.
This is why I'm okay with Lowry as a 3rd line centre *with the right wingers and deployment*.
The best I ever saw Lowry was when he was with two of Frolik, Stempniak, and Perreault.
Last season rankings in EV Offense per min:
Perreault 20th
Stempniak 158th
Frolik ranked 160th
Matthias 257th
Armia 250th
Dano 278th
Copp 280th
I think Lowry can be on a 3rd line that does very well, but Matthias and Dano had weaker EVO/60 years than norm, and Armia and Copp haven't shown to drive offense at the NHL level (at least yet).
If you are putting him with guys like Mathias, Armia, Copp, and Dano (and these players don't improve offensive driving over last season), I would rather the Lowry line as a fourth line.
If you are putting him with guys like Perreault, Ehlers, Connor, etc., I would rather the Lowry line as a 3rd line.
I think this would if you got one player from each group, third line would still be optimal deployment for Lowry.
That's the way I look at the numbers and interpret the optimal usage from them.