In fairness, Russell had a high usage rate as a rookie on a bottom three team. Rozier did not have that opportunity.
Russell's upside is limited due to athleticism and defense. He has fantastic court vision and projects to be a really good shooter (not elite but really good). He should fill up box scores and impress espn with his numbers, but when the rubber meets the road and he has to create his own shot or make a big defensive stop, in his prime will he be able to do that? As a Celtics can, hopefully not.
On the other hand, prime Rozier could be an elite shot creator/driver and defender. Even when he was drafted, I felt confident that his shooting and passing would improve with reps, and he has already shown improvement. In other words, Russell doesn't project to be good at Rozier's strengths (defense and shot creation) but Rozier projects to be good (shooting) and passable (court vision) at Russell's strengths.
There is not another player in the NBA who relies so heavily on step backs and jump shooting because they can't get all the way to the rim. That could be bad or Russell, or he could be creating a new archetype.
Anway, that's the argument for Rozier. Not sure I agree with it, but it's not totally without reason.