Yes there's a difference. Dominant implies they beat you all 48 minutes. Not the last 12. The last 12 indicates depth that overcomes the better team getting tired.
4-0, maybe 4-1, is dominant. No excuses need to be made if the team really is dominant.
One of the best ever means you sort the teams by record. The Warriors were the best ever in that regard.
The dynasty Bulls won 3 championships, missed 2 with prime Jordan playing baseball, the three more. I say they win the season before if Pippen plays game 7, and the two years Jordan missed. That would have been 9 in a row. But no excuses. In those 6 seasons, they won 72, 69, 67, 62, and 61. They won 55 without Jordan.
As good as the Bulls were, they lost to the Pistons 3 straight times. Those Piston teams were damned good.
Assuming the Warriors win this finals, we can talk about greatest ever after they win 60+ 5 times and 3 or 4 more championships.