Jaylen Brown seems to have a high acceleration. The opposing team should have help defense. To the Pacers' credit, they did their best to defend Brown for me. If there's help defense, does he have good passing and court vision like Doncic? If no help defense, he can rely on his acceleration to score repeatedly.
The Pacers should have been able to dominate the paint, because they have bigger and stronger players.
If anything, I think the Pacers did a good job resisting doubling. The Celtic's strategy is to always have many shooters on the court. Normally they would be able to probe the defense to draw a double team and then send the ball around to the uncovered player. To me, it looked like the Pacers kept everyone covered and guarded passing angles. Many of the Celtics possessions ended with the ball handler looking for an opening for 15 seconds and settling for a loosely contested 3.
My fear for the Pacers is that the way they lost game 1 and 3 is going to haunt them mentally for the duration of their careers. Celtics are going to be a mental road block for them.