There's a reason why phoebe consistently holds the top spots in the leaderboards. Melee heroes have so many more shortcomings in this game.

There are only a few bosses that are difficult to kill as Cloud and Rondu. Itemization is really important for these heroes.
While playing Rondu, my issue is usually the Keeper of the Light that can trap you in the black hole and the Dark Seer, so I ask my teammates for help on these. Anything else I can destroy. If itemization isn't the issue I suggest attempting to kite and learn skill patterns. Gl