It's not a solution, it's a tool.

If the enemy discovers that 500# wont work they'll go to 550#. NO DEFENSE is perfect. The best possible defense is to stay on the offensive. And no, offensive does not necessarily mean violence, it means seizing the initiative and forcing the enemy to react to you, rather than vice-versa. In the present case we increased violence a little but mostly (and finally) empowered local people to deal with local threats. Now the enemy must react to locals who have rejected them. That is why the violence has dramatically dropped in Iraq. Not MRAPS.