These same models of Pelton's also have neither LA team in the top two out West, have Houston as best in the West and has Orlando 4th in the East. What is surprising about Boston being #2 in the East isn't that Pelton thinks Boston will be great as they only project out at 47.4 wins by Pelton's model. That's about where a lot of models, projections and betting lines have the Celtics, within a game or so.
So Pelton's model isn't saying Boston will be a great team, he doesn't even have them at 50 wins. But he is saying the Sixers are not going to be as good as most think and that the East is dreadful as compared to the West.