Good point
Hi Nick
Any alternative that's viable instead? Remember Ringwood's "Rock Vapour Disk" concept of Moon formation that had the Earth enshrouded in a flattened disk of condensing silicates? He gave that idea up for something like the Big Impact, but involving several asteroids sending material into orbit over time.
Some very fine minds have wrestled with this problem - should be be so surprised that we can't crack it on a discussion board? I think the Trojan planet idea still has a lot of mileage, but who knows?