And I think the general consensus is "No, it's not overpowered". Yes, it's very powerful. In one situation. Yes, it can completely turn a battle around. In one situation.
Lead the Attack is the definition of a specialist power. Is it useful in fights against non-solo monsters? Sure it is. But nowhere near as useful as, say, Bastion of Defense. But solo monsters (or other "boss" targets) are obviously what it was designed to handle.
I mean, solos have higher than normal defenses, along with higher than normal HP. Lead the Attack has to break through those higher than normal defenses. So chances are, your Lead the Attack won't even have a 50/50 chance of connecting (barring outside influences to your attack roll). Missing gives a much smaller bonus (though a bonus I'm sure will be appreciated all the same).
It's risk vs reward. You're putting a big investment (a standard action and daily power) into a chance of having a powerful impact against a single creature. That seems to me well balanced for a daily power.