Well, comparing Arena to Battlegrounds...

You are not limited to the number of arena matches you can play in a given week.
So, in theory your team can gain or lose a lot of points over the course of a week.

In battlegrounds, we will be able to gain points six times in a week.
Not sure if that means the first six games will count, and after that there is no option for rated play.
Or if we will take the points for the six best games over the course of that week.

They did mention it will be impossible to lose rating in battlegrounds, which is a big plus for BG's.

Not sure if they'll cap the amount of arena you can play for points in a week.
If placing a limit on BG's, to prevent it from being a grind is their direction, arena can be just as much of a time sink over the course of a week.