But is the Celtics’ success sustainable? While Boston’s lineup is littered with knockdown shooters, unselfish ball-handlers and tenacious defenders, it also lacks size, especially compared to the lineups deployed by other Eastern Conference contenders, including the Philadelphia 76ers, Milwaukee Bucks and Toronto Raptors. It’s fair to wonder whether this could be an issue come playoff time. “Would I favor them in a playoff series right now against Philly or Milwaukee? Maybe not,” one scout recently told ESPN’s Brian Windhorst. “You can focus on what they don’t have, but if you look at what they do, you see they present you a lot of problems. Who knows what the matchups will be or who will be healthy in the end.”