I feel the best word to describe Boyle potting 20+ is "mistake." While it's great he had a season like that, he's not even remotely close to a 20 goal scorer.
Hagelin is a fine player, he does the little things right and can certainly contribute significantly for a lower line player. That being said, IF he ever were to pot 30, i would consider it Boyle-like, in that it would be a "mistake."
The poster I quoted referred to Hagelin scoring 30 goals multiple times. The guy is not a 30 goal scorer. This year the NHL, had 21 30+ goal scorers. Every single one of those guys is basically a bona-fide star, outside of maybe Kunitz and Patrick Sharp (who are both better players then Hagelin AND play with elite players).
Hagelin has yet to show he is a 20 goal scorer, he also was not a young rookie. He will be 26 for next season and while that's not old, he is showing what his make-up is. I fully expect him to break 20, on multiple occasions, but to hint at or even expect 30 is not fair to Hagelin nor yourself.
We as fans tend to significantly overrate players, which is why it leads us to value them, often, negatively (see: Michael Roszival).
Hags is a fantastic guy to have in our Bottom-6. He's the kind of guy that helps you win in the playoffs. He's the type of depth you need on small contracts in today's cap NHL. But at this point, I think it's very clear what he is. A very good 3rd line player, who can slot in on the 2nd line, kill penalties and spark the offense with his speed.
I really like Hags, but to hear people talk about him scoring 30 is a shame and will no doubt lead to this guy becoming a whipping boy.