Yeah, Rozier might turn into a decent player, but it looks to me like a safe bet that Portis will end up having a more significant career.
It's true that the Chicago situation is different than Boston, but they were still loaded with veteran bigs vying for playing time and yet they were looking for reasons to work Portis into the rotation early on this season, before Noah had even gone out for good. Portis has good size for either big position, can rebound, defend at least a little, and seems to have some range. He's got a role in this league, in other words.
Rozier ... hard to say. In the limited minutes he's gotten, he looks to have the physical ability to compete at the NBA level. He's pulled down a fair number of boards for his size.
Looking back at the draft, it seems Ainge reached for a long-armed combo guard who's active on the boards and in man-to-man defense, but who has no true position and may or may not be able to shoot.
Shocker.
Oh well, not a make-or-break, just like the Young versus Hood thing. Hopefully Rozier actually becomes a guy who can be relied on for rotation minutes, unlike Young.