So does 'Solomon' benefit from Chaldea collecting the grails or something? Even if you're confident that they won't ever be able to beat you and that you can kill someone at your leisure why not save the effort of tracking them down later or whatever when you can just... kill them all now when you're already there? It doesn't matter that you're thankful one of them accidentally did you a favor, if you're all "Haha, I am so much better than you that I'll let you go this time but you are totally dying in the next singularity anyway, I know that for a fact! Also I'll save you the effort of looking for it, it's in your homeland."