You're comparing Norris's best season in 3 years to Pettersson's worst season since he entered the league.
Norris's career PPG 0.64 | 30 Goal -53 point pace.
Pettersson's career PPG 0.98 | 32 goals - 80 point pace.
Petersson's peak is 102 points while Norris's is 55 points.
Not to mention health and availability.
Despite only being a year older Pettersson has played almost 2x amount of NHL games as Norris (231 vs 450). Pettersson only has 1 season where he played less than 68 games a year, where Norris has yet to play more than 66 games a season.
I love Norris as the next guy but I would have no hesitation to ship him out for Petey, he's on another level in terms of talent level and production, he's more on the Stutzle level than the Norris one.
I have no concerns about his recent dip in production as its clear that its the environment around him having an effect on his play, and this is another Eichel situation where the player will produce back to normal pace when he's out of that toxic environment. Dude has had 6 seasons of straight elite PPG production, he hasn't suddenly lost it to an injury or forgot how to play.