So their methods are a little unorthodox, doesn't mean they weren't good diplomats.
And you know I'm kidding, right?
You're right, there's no IGO-type body in the Trek-verse, but all the non-corporeal/super advanced aliens are as close as they've come - and who's to say not better than a simple mediating party, since they can actually do something
to stop the fighting.
But then you get into that whole free will thing, and that never ends well.