Tag arena is needed to get the legendary in the missions, so it's got to be done till  you hit gold 1. Truthfully wish their was an option to remove your def team when you hit gold.

Live to be fair, once you do what you are doing you can just not play, but then because of that reason it's been added to daily tasks, frankly it's clearly not that popular or it would sell itself.

Arena itself is necessary to play to keep your bonuses, I feel that's the reason why people field such easy to beat teams. I would happily take that on the chin to remove my def team.

Once the teams are removed they should be taken from the task section. As we are told how spiffing and popular arena games are to the community, anyone who wishes to withdraw from them should be able to, without be penalized.