I suppose there is a happy medium somewhere between bees that are "too hot to handle" and bees that are "too mild mannered for their own good" and I don't think either extreme is advantageous to either me or the bees. I certainly don't want bees that follow me 500' to my house and wait around outside for me (or anyone else) to come out so they can attack, and I don't want to sustain a relentless assault by hundreds of bees when I pop the lid. On the other hand, I don't mind high-spirited bees.
I've also noticed that my bee's temperment varies depending on the time of day, the weather, and the season. I don't bother my hives after 6 pm and they don't bother me. I leave them alone on rainy days and they leave me alone on rainy days. In late summer when the dearth arrives, I put on my gloves and they take their's off. I cut them some slack. We more or less get along.
That said, I do think there is a connection between overall fitness and aggressive behavior. The question is, where do you draw the line?
When you say you have one hive that is "extremely aggressive" bluegrass, just what do you mean?