I did these arcs to see what the fuss was about - the Protect the Henge finale is clearly broken. Am I the only one who remembers it being challenging? I think the retail developers must have nerfed it at some point because players wanted it to be easier. In the old days, a pause of a few seconds between waves was necessary in order for crowd control or knockback powers to recharge, or to give time to place caltrops or trip mines. It wasn't possible to aggro an entire spawn; they were too intent on their goal, the henges.
Now they don't care about the henges at all. When I got bored on this mission, I placed my blaster near their path and watched the next spawn stop and fight, even though I wasn't doing anything. I read a book for 10 minutes, only healing my character when he needed it, and succeeded at the mission.
There's no reason other than nerfed AI to make the Red Caps care about a hero who isn't trying to stop them. I think the threat level or whatever it is of the henges should be bumped up to what it used to be, then the mission would be challenging again.