The AL East being a good division does not hinge on some teams being superior and some teams being inferior. The point is that all 5 teams are over .500 and very competitive. My point is what you said in the bold.
The problem is that you're judging the teams in the AL East by comparing them to the average of the teams in the AL East, and nothing else. If you use the rest of the AL, you'll see that there's 9 teams in the AL with a .500+ record, and 5 of them are in the East. And it's not like they're all hovering around .500. The Rays have the 2nd best record in the league. The Orioles have the best Wild Card record, and the Yankees are tied for 2nd in the WC. And all of this is with a huge amount of injuries in the division. It's clearly the best division in the AL.