Honest question. Did we draft Poulin in the first round to be projected as a 3rd liner?
No. Teams don't draft a forward 21st overall if they think he's going to be a 3rd line guy, unless they see him as a super high end Selke-type 3rd line guy (this was kind of the hope/projection for Phillip Danault when he was drafted, as an example).
The Pens were high on Poulin. They may have been wrong or they may have been right, and it will likely take another 2, 3 maybe even 4 or 5 years to find out. But there's no question they saw a guy who they thought was a top 6 F.
If you're sitting with the # 21 pick and your scouting staff don't feel there are any top 6 F left on the board, then you should trade back and try to get a later 1st + 2nd or 2 picks in the second round.