Yeah I don't even know. It's wierd. The idea for leagues was to separate player pools to match skills levels, but they don't even do that, that's a completely different match making system... so I don't really know what the point of that is anymore besides having a cool Diamond badge on your profile.Also the ranking system is stupid. And they do a poor job of documenting it. So I'm #1 in a gold league... what does that even mean? As far as I can tell it means that I'm actually a crappy gold league player because otherwise I would've been promoted before I amassed enough points to rise to the top of my league.
I agree that leagues are completely stupid and best ignored, but the different divisions work pretty well. The point system also works well, but only once you've reached diamond. Before that, just ignore the point system.