The Celtics' titles of those years are discounted simply due to time. It's like, I think it was Bob Ryan, wrote " you hear the word athleticism so much today that you would think the players of the past couldn't run or jump". Imagine if you told a young person today that a player was coming into the league who is over seven feet tall, can bench press over 500 pounds, has very close to a 50 inch vertical and will score 50 a game for a season. Noone would believe it, just as they don't believe that the C's so thoroughly dominated the game in the period discussed.
In 30 years, or less, there will be a player come along who will make MJ look no better then Dominque or Barkley. That player may not really be as good as MJ, or for that matter Dominique but people will have forgotten how good MJ was. How many people thought Shaq would destroy Wilt? If you don't think that is a fair comparison, think again.