Always until it is done. It is not done.
That said, the coach isn't shooting terrible shots and missing. The coach isn't making bad passes. The coach isn't defending the other team. It is easy to blame the coach when things go badly (Milwaukee did that as well), and Joe is obviously a young coach that has made some mistakes, but he isn't on the floor missing shots, turning it over, and not defending.
Also, while I thought Boston would win the series, I was concerned because Embiid is the best player in it by a pretty wide margin (if healthy - and he is pretty close to 100% now) and the Sixers have a lot of solid good fitting talent around him. All of that matters, especially in the post season. And while Tatum is a better player than Harden, Harden has been the 2nd best player in the 5 games of this series. That matters even more. Maxey and Harris are excellent 3rd and 4th options and Tucker, Melton, Niang, and Reed are at least competent.
The Celtics depth has been greatly overstated by this board and the media all season. The guard depth is excellent, but the team really only goes 3 deep down low with Horford and the Williamses. Tatum plays PF way too much because there just isn't anyone else. It has been a disaster and a team with Embiid is just too much for the C's to handle. Even with that though, Boston should have won this series in 5 games. The guards and wings have been the problem as they just can't consistently shoot and the defense on Harden has been awful.