These games definitely magnify the glaring defensive weakness of the Suns. The Mavs crushed the best defense in the league (Minnesota) only to be crushed by what appears to be an even better defense in Boston. Boston can even being missing their best defensive piece and still win. And they can win without even shooting well. Against Suns, it would be a slaughter of biblical proportions.
Boston has the #3 defense. I think they're better than Minnesota also. They've blown more teams out and won more games as well, which I believe could cause a disparity between them and Minnesota. More garbage time allows for inflated offensive numbers for their opponents and lower defensive stats for them. I could be wrong. I've always felt the difference between the top 3 or 4 defenses, or offenses, are negligible. They're top tier across the board.
A key difference is Boston's defense is the same as it was all season while Minnesota struggled some due to teams pulling Gobert out of the paint. The game changes in the playoffs and Boston hasn't needed to adjust while Minnesota failed to adjust.