Hero Vs. Legendary

Before I start anything... I may used the wrong Terms or words for those things!
Hero: The monster in a dungeon that you face at the end of it. (Usually drops a HERO Item)
Legendary: The monsters you see in different parts of the dungeon, and they are normally surrounded by Rare monsters. (Usually drops a Legendary Item)
In DBO, I used to play with my guild mates a lot, we used to go dungeons most of the time, and I just know that we had a harder time dealing with Legendary monsters than the Hero monster...
I mean a HERO monster should be VERY hard to KILL, but it is usually easy! However, Legendary mobs are hard to kill, but they are VERY HARD!
My friends and I would nearly all die trying to kill Legendary mobs, even after planning our moves! And HERO ones were like a no sweat battle to us!
Did Anyone had the same thing happen to him?
And Will any Development change HERO and make it more Challenging, or make Legendary LESS challenging?!