It's tough, hard end to the season (if it is the end).
It is one of the risks of having an overachieving regular season team in a relative down year in the East with a team largely of smoke and mirrors; you run the risk of increased expectations and thus increased disappointment upon falling short.
I mean, IT is a great offensive player, a minus on defense, who has been on a few teams. Bradley and Jae are solid, should be role players, not much more. Amir should be a bench player, same for Olynyk. Horford should be a veteran 3rd banana type at this point. Smart is what he is, net negative on offense, good D. Jaylen is a rookie from the worst draft in recent memory.
If the Celts were in the west, they'd be the #4 seed, losing in a 4-5 matchup with LAC, and no one would be surprised.
And that is using their "actual wins." If you look at more predictive numbers, they only had the 3rd best point differential and 3rd best net offense/defense in the East, behind Cleveland and Toronto. Their overall point differential would suggest a team that "should" have won 49 games, tied for 4/5 spot with Washington in the lesser East, and 49 wins would have been 6th in the West this year.
So I think the stretch of "great" 4th quarter wins gave us a good record, but contributed to the smoke and mirrors; we're just not that good, one of the weakest 1 seeds ever, probably.