And we're saying even though Marcus has one of the worst offensive ratings in the league the offense is somehow BETTER when he's playing? How in the world does this happen?
I am not saying it, it literally happened last year. When Marcus Smart was on the floor the Celtics offense was more efficient than it was when he was off the court.
This also occurred during the playoffs.
https://www.basketball-reference.com/teams/BOS/2018/on-off/
Now raw on/off numbers are tricky, but they do indicate that Marcus wasn't some disaster for the C's offense as you believe.
Yeah ... um ... you really have to take these numbers with a GIGANTIC grain of salt unless you actually dive into the details.
For example, you need to consider things like, when Marcus was on the floor about half (48%) the time Kyrie was also on the floor. For Rozier, Kyrie shared the floor with him on just 22% of the time.
Sharing the floor more often with a guy who is not only an elite 60% TS high efficiency scorer but also a very high, greater than 30% USG scorer, will tend to do wonders for your offensive rating.
minutes poss ORtg DRtg Net (per 100)
Marcus w/ Irving 837 1667 117.4 104.6 +12.8
Marcus w/o Irving 936 1827 103.8 103.5 +0.3
Rozier w/ Irving 531 1049 112.4 109.5 +2.9
Rozier w/o Irving 1900 3689 108.4 105.7 +2.7
It's important to really look at the details of who is sharing the floor with a player when looking at ORtg and DRtg and on/off number.
I think it's important to look at actual 5-man data to see what it tells you. The difficulty there is getting samples of sufficient size.
Marcus' most commonly used 5-man unit was with Kyrie, the two J's and Al.
Rozier's most common 5-man unit was with the two J's, Al and Aron. Here is how they performed:
Unit minutes possessions ORtg DRtg Net (per 100)
Kyrie+Smart+Jaylen+Jayson+Horford 140 281 116.2 112.7 +3.5
Rozier+Jaylen+Jayson+Horford+Baynes 163 306 111.0 100.3 +10.7
Unfortunately, the 'swap' units of Smart with the two J's, Al & Aron (just 45 minutes) and Rozier with Kyrie, the two J's and Al (just 49 minutes) are both too small to be useful as comparisons.