I was wondering, right now the Grand Arena is strange... The only thing that counts anything is to clear the board. All the points come from clearing the board. Also most of the additional currency is coming from clearing something a special way.
This makes Grand Arena really boring. The way to go is to set aside your six strongest attack teams and destory everything the enemy has. The rest, you put into defence.
Until now I have never lost against someone who prefers defense. Maybe I don't clear the whole board then but I get more points than he is because most of the time they don't have enough attacking teams.
I would suggest to make a small change which could make everything better:
Give players at the end of the fight points for every area they haven't lost. This does not effect players which can play both offensive and defensive at the same time but enables more strategies for players with weaker rosters.