I think given their records, point differentials, strength of schedule, type of schedule, if the Sixers are struggling, then so are the Celtics. I wouldn't label either team as struggling, though. They are both on pace to have 56+ wins.
Both teams have issues, whether it is lack of size, injuries, shooting, needing to load manage players, getting off to slow starts, whatever. But, I think it's something both teams will address and get better as the season progresses.
Both teams, IMO, are 55+ win teams this year.