Looking more at this ON/OFF +/- thing. The idea is to normalize everything to 100 Possessions. That is fair. You could normalize to 36 min or something else, but 100 Possessions is fine.
In Game 1, the BOS overall team had a net rating of +20.4 (there were only 93 possessions in the game so the 18 point win gets adjusted a little). So the theory is that for any player that had an individual net rating lower than +20.4 would be an indication that the team was better when that player was off the court. The individual net ratings for Game 1 were as follows:
Hauser +53.1
Holiday +30.8
Porzingis +29.6
Tatum +23.2
Team +20.4
Brown +17.8
Pritchard +17.1
Horford +16.3
White +5.9
I didn't bother with the garbage time guys. So as you would expect, half the regular minutes players were above the team NRTG and half were below. One game is a small sample size so there is some distortion.
For the entire playoffs, the team is +11.5 NRTG. Hauser, Horford, Holiday, and Tatum are the top 4 above the team line (in that order), Porzingis, White, Brown, Pritchard, Kornet are below the line (again ignoring deep bench players).
If you go by this, Hauser, Horford, and Holiday are all better in the playoffs than Tatum, Porzingis, and Brown. It makes no sense. Extrapolating to 100 possession for players who don't play much (like Hauser) will amplify their impact but Hauser is way up and Pritchard is not.