That's because the game is designed to need healers and tanks. It's not hard to adapt that fight to make it not require a tank nor healers...
Basically it's relatively easy to port the "mechanics" of that fight over to GW2. "tone down direct damage" is probably the easiest... Make the boss deal X% more dmg if he isn't kited to the proper area (think about the boss turning red, green orange, blue, and the floor having different zones with corresponding colours where you need to "kite/dance" the boss over inorder to remove a boon on the boss or something...
The "mechanic" is only the move from this zone to the other zone consecutively and then back... That mechanic is easy to implement in various ways.