When you're only shooting 2.65% on the road, a season after shooting 8.94% on the road, it's safe to say that you probably just haven't been very lucky on the road. Likewise, when you're shooting 16.91% at home, a season after shooting 13.39% at home, you've probably been on the slightly pleasant side of lucky.
And +/- is a team stat. Bad goaltending, a young developing defensive center, and some sketchy bottom pairings all contribute.
And when he's so productive at home, it doesn't hurt either. Let's put it like, in the last four seasons, these are the players to have scored 52 home points:
Sidney Crosby - 2013-14 (Art Ross Trophy, Pearson Trophy, Hart Trophy) 56 points in 40 games
Johnny Gaudreau - 2015-16 52 points in 36 games
Oh, and Gaudreau still has four home games left to play (he was scratched for one already otherwise it would be five). Patrick Kane has 47 home points this season.
Last season Gaudreau was 82.857% as productive on the road as he was at home.
If Gaudreau were as proportionally productive on the road relative to home this season as last season, he could have 39 road points and 91 total points in 69 games. That'd be a 59 point pace at home, 48 point pace on the road. 107 point pace on the season.
He doesn't, he's on a mere PPG pace (if he continues his road/home splits he should finish with ~80 points in 81 games). That's what we're judging him on.
It's unfortunate that he's not on a 107 point pace but 107+ points has been done exactly once since 2010-11 by Evgeni Malkin and he had a sweep of the Hart / Pearson / Art Ross that year. If I'm correct Kane is on pace for around 104 points and will run away with the Art Ross this year.
That's how dominant Gaudreau has been at home.