[quote=Asuras]
Sure, a million space rocks would be difficult to stop. But to say you have the capability to fire all of them means you surely have the ability to make a lot more standard missiles. If you have a million space rocks (you'd need the rockets to propel them, likely many per space rock), then I'd have several times more explosive-carrying missiles. Stopping your space rocks would seem like much less of an issue, then.In the scenario you described, you say you "bring in your fleet" as if it were some freebie. If someone had the power to stop a fleet much larger than your own of space rocks, then I'd have to assume they have the power to take on a fleet as well. The protection of Earth from space rocks could occur from the planet's surface itself (or other Sol system planets); no space fleet required. With your rocks gone, you only have your fleet to use, which is now at the mercy of the Earth-borne fleet given you've "brought them in".
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You have X number of Space Rocks. Each has 4 Rockets. (for simplicity) lets go with 1'000'000 Space Rocks. So you have 4'000'000 Rockets attached to your swarm of Space Rocks to conduct your bombardment. 

Each Space Rock is 1km across at smallest. It would take the enemy their heaviest weapons to destroy your Space Rocks.

Person 2 just sends 4'000'000 missiles.

The Defender can destroy each missile with one shot from their point defence.

In the end it is infinitely more likely there would be big space rocks left over than missiles.

(OH, and the whole each rock has 4 Rockets is for maneuvering. As they ARE space rocks, you don't need more than a single rocket to get it moving. The others are only needed to adjust the course.)