I think you're right on that Rilla, a PW would take a lot of work. Perhaps even more than its worth with how high of a rotation Arenas seem to have with Players. 

If we take out the PW then adding in Tiers is something incredibly easy to do. Stick with the three that were mentioned earlier and let players work out the details between them. Maybe offer more points if someone of a lower tier beats someone in a higher tier, and less points if someone in the higher tiers wins. 

Or, you could just restrict it so you have to stay in your Tier, than have three seperate 'point' systems for each tier. But, you could still record the overall Win/Loss Ratio.