This is because Berube plays a more defensive style.
Teams that play run in gun give up a lot of goals becaus their forwards are always looking to break out.
Teams that don't give up a lot of goals and play back rarely score a ton of goals since the forwards are focused on defense.
Changing your style of play can manipulate your players stats.
It can manipulate your stats... but more as a team and less as individuals... you are talking the guys who are the majority of your offence (so 70-80 point guys, generally generating around 30 % of team offence) losing 5-10 points from a run and gun to defensive style.
Among similar teams (talent/point/position wise) you are talking about 25-35 goals a year less between a run and gun and defensive system.)
So if G had played in a more defensive system over the last few years he would still be expected to be approximately PPG.
The problem though is when players are on legitimately poor teams... the dropoff team wise from being an average playoff team to bottom 5 in goals scored is another 30 goals... so if your team goes from a good team who are offensice to a bad team you probably lose another 10 points off your 1st liners... so 85 point guys become 65-70 point guys.
It should actually affect guys who get less points less as well, so their end of season point totals look respectable, as a similar % drop off is only a few points for them (so 55 to late 40s, as they are involved in less % of team offence)
On bad teams point totals usually seem to show the better players playing worse (just off stats, if not actually watching games) due to this, and 2nd-3rd liners not dropping as much.
Ofc that is really simplified and not accounting anything but past averages, just looking at teams, goals, obviously more offensive teams and more defensive with similar point totals.
If the Flyers keep the abysmal offence up a good season team % wise for G will be around 45 points! (1.57x 82= 129/3= 43... that would be over 33% of all team offence, (34.9%) more than he usually is!)
That is how bad the offence has been!
Ofc G is a part of this, and that has to be factored, but he is still being involved in a similar amount of team offence as he usually is.