You just did exactly what I said - taking one random game can be a fluke. When it's a regular pattern it is different.
So far this year the only guy in the Pelicans top-8 with a worse +/- is JJ Reddikk, and he's missing everything he shoots and getting killed on defense. And I'm not saying that the Pelicans are terrible with Zion on the court, they're only slightly worse. But why are the worse at all when he's getting buckets so easily? That's the part that is crazy to me. Sometimes +/- can be gamed because you're always with the same players, so a weak supporting cast brings you down. But that's not true with the Pelicans, Zion if anything gets to play with the best lineups on the team. So why is their performance so weak?
Zion runs the score up against really shytty teams. Last year he was +25 in a game against the Grizzlies, +20 in a game against the Warriors, +21 in a game against the Cavs, and +20 in a game against the Timberwolves. Those were four of the worst teams in the entire league and they were all basically playing for the lottery at that point in the season. Take away those four games and the Pelicans were -25 when he was on the court despite really gaudy offensive numbers. I don't think they're worse with Zion on the court, but it doesn't seem like his impact is as big as his scoring numbers make it look because he keeps giving it back.
And it got worse as the season went on. Here are the last 10 games of the year.
Lakers: Zion goes 12-16 for 35 points, but team is -10 with him on the court and +2 without him
Timberwolves: Zion goes 10-19 for 21 points, team is 0 with him on the court and -5 without him
Mavs: Zion goes 9-18 for 21 points, team is +1 with him on the court and -5 without him
Heat: Zion goes 7-9 for 17 points, team is +1 with him on the court and -6 without him
Timberwolves: Zion goes 9-16 for 23 points, team is +20 with him on the court and -7 without him
Jazz: Zion goes 6-8 for 13 points, team is -16 with him on the court and +14 without him
Clippers: Zion goes 3-7 for 7 points, team is -17 with him on the court and -6 without him
Grizzlies: Zion goes 9-21 for 23 points, team is +8 with him on the court and +2 without him
Kings: Zion goes 10-12 for 21 points, team is -12 with him on the court and -3 without him
Spurs: Zion goes 10-20 for 25 points, team is -21 with him on the court and +12 without him
The only time in the final 10 games that the team really outscored opponents with Zion on the court was against those awful Timberwolves and Grizzlies teams. In the other 8 games the Pelicans were a combined -74 with Zion on the court but +3 with Zion off the court.
If you think Zion is playing well on defense that's your prerogative, but even you're suggesting that half the time he's out of position it's the team's fault and half the time it's his own damn fault.