It might be early, but point differential is one of the best indicators of success. Last season at this time, many people were looking at the Warriors point differential and doubting whether they were for real or if that stat isn't a good indication of success.
Maybe the Celtics are overperforming, or maybe the games where they got blown out were the result of inconsistency from losing a starter to injury and figuring out continuity and chemistry.
The Celtics are not the Warriors, and I don't think they have been consistent enough to be a true contender, but this negative narrative about the limits of the starless Celtic team is getting tired, and that tired narrative is not jiving with reality on the court or in the advanced stats.