As others have mentioned, Tierney's individual shooting% was lower than his career average last year (by ~4%), but his on-ice shooting% was high (by a couple %).
His deployment was also drastically more difficult in Ottawa. He was buried beneath all the star centers in San Jose, so while his quality of linemates was weaker than in Ottawa, his quality of competition was that much weaker still. While he did see powerplay time and significant minutes with Stone and Tkachuk, he played a lot more with Boedker, Ryan, Paajarvi and Balcers.
Based on the ol' eye test, it seemed to me that his hockey IQ is very good, and that he recognizes he isn't a high-end skilled player, so in the offensive zone he was always much more inclined to just make a smart, simple play to keep the offensive zone possession alive, rather than trying to make a play on net. This had a lot to do with his low shooting%, and it also had a lot to do with Boucher loving him and leaning on him so much.
Personally, I'd have liked to see him take a little bit more initiative offensively, but he was given a role by the coach and executed it to perfection. And really, that's exactly what is so great about him. He's a soldier - a team guy first, going back to his junior days playing for a powerhouse team in London, he was there for all three years of the dynasty, and started in a checking role then worked his way up, and was named captain and put up 40 goals and 80+ points when he was counted on as a 19 year old.
Then he came into an offensively anemic Worcester team and was immediately counted on to provide offense as a 20 year old. He did not disappoint, with 29 points in 29 games. In San Jose he played the checking role he was needed to play behind their star offensive centers.
I wouldn't say he was snake-bitten last year, but it was his first time given any sort of offensive responsibility at the NHL level, and he came through while still putting defense first. I would assume he'll be spending this summer working on offensive skills, and he still has room to grow in that regard.
Depending on how the new coach uses him, he should be somewhere in the 45 point range again this year, and I don't think we should be surprised to see him take a other step forward with his offense.
You were comparing him to 2nd liners and 3rd liners, I wanted a general assessment of his vision. Now I have it, though I don't quite understand it. 
