For the Celtics in 5 crowd: Is the assumption they lose game 3? Or do you think if the Celtics win game 3 the Mavs will be able to win game 4?
Don't have a prediction on which game, but I'd guess that Dallas has one night of punching above their weight class in them. While teams that are ahead in seven-game series can have a night when they (inadvertently) ease up a little. Put those two together, and like the Miami and Cleveland series, I'd guess the Mavs take one from us before it's all said and done.
In favor of the sweep: all the things that people have already said. Combined with the fact that this Celtics squad seems to get the yips more often at home and then settle down on the road (maybe this will change after they get their first ring, and ghosts don't loom over them as large?). It wouldn't surprise me at all if shots start falling easier for Tatum once he gets out of Boston.
On the other hand: Dallas has been through a lot, their pride is hurt, and role players classically play better in front of big home crowds. The Mavs are going to have a few punches left in them before they go gentle into that good night (if they ever do). We're (over)due for an insane Kyrie Irving game, and while I'm not surprised that he once again played below himself in Boston, get him back in front of his adoring fans in Dallas and there's a decent chance he shows why he's once of the very best in the league at shot creation and shot making.
Long story short: I think Dallas has at least one lights-out, low-probability, incredible offensive game in them. And it's coming.
Of course, we might sweep them before they get around to having it. I wouldn't object.