The Lakers not being an elite defensive team won't matter because the Celtics are NOT a great offensive team.
Don't throw regular season stats at me, I'm talking about the playoffs. Playoff basketball is a totally different beast than the regular season and it is the only thing that is relevant right now. The bottom line is the Celtics score in the 70-80 pt range just as often as they do in the 80-100 pt range. Hell I've even seen them put up a pathetic 69 pts.
Hate to tell you this but the old adage doesn't go
"Offense wins championships!"
Celtics averages this postseason: Scores 91.6 Gives up: 87.3
Lakers averages this postseason: Scores 105.9 Gives up: 99.5
One team dictates the tempo through offense and the other through defense.
The Celtics have played against two stiflinf defenses already and I don't see where the Celtics offense couldn't suddenly get very healthy against a defense like the Lakers that allows lots of looks and baskets.
On the other hand, the Lakers haven't yet seen the type of defensive pressure the Celtics play so far this postseason. Not even close. The Spurs were a great defensive team this regular season but weren't even close to performing to their regular season capacity in the playoffs.
The Lakers might take one or two too many games getting acclimated to being hit, clutched, grabbed, knocked to the floor, constantly have hands flying at the ball during the shot and dribble, and the relentless no stop action of this as the Celtics bench brings the same defensive intensity.
The Lakers had better hit their free throws because there aren't going to be any uncontested drives to the basket.