I don't think he beats out Cartwright in the first run. I'm not sure he beats out Longley as a starter either. But I think he could have been a prime backup on either team. Those guys were both much better as 80s/90s centers than most remember. The Bulls didn't need point production out of their starting centers. They needed guys who could rebound, play defense, and fill their role moving the ball around, screening, and getting an occasional bucket on offense. Watching the Last Dance documentary, I thought Longley came across as under-appreciated at the time. He was able to do enough to be a net positive on a team with the brightest star ever, one of the best defenders ever, and a rebounding machine "diva".
Also keep in mind the era. I love Luka, but he would have gotten eaten alive by the like of Shaq, Ewing, Hakeem, and Robinson. Then there's Mourning, Mutombo, and Divacs in the next level of players he would have likely had issues with.