We saw what Fournier was for Boston, i.e. a 13 ppg bench player
... while recovering from Covid, which severely affected his vision, and presumably his conditioning.
We've also seen what he has been in New York: 17.5 ppg, 45.1% 3pt%, .564 eFG% for the best team in the NBA so far.
He's scoring more than Smart (7.4) and Richardson (7.4) combined.
Once Jaylen Brown recovers from Covid, the Celtics will be fine.
"Fine" isn't the goal, though. And, even when Jaylen has played well, the rest of the team has let him down.
There are management decisions that can be questioned if we want better than "fine", which probably equates to 6th or 7th in the East.