Short Answer: Yes, its broken.
Long Answer: Those who stretch to find ways to get around the brokenness of this power are to be commended, because they're engaged in exactly the sort of thinking and reasoning a game like D&D requires. But ultimately the power is still broken because the potential countermeasures are too tenuous and strained. As a general rule, if a single power requires you to alter all combat encounters just in case the players use it, it's broken.
I agree with this statement.
In my current game, I just stopped using melee minions because they die much to quickly (There are too many AoE powers).
I have previously commented on Rain of Blood being overpowered, but I think it is ok-ish, because it targets Fort and doesn't hit that much. It will surely hit one mob, and that mob will hurt, but that isn't a big problem.