I just noticed that a line up that buffs each other's damage in arena is far more effective than a team that focuses on defence.

It seems like the damage formula and defence formula in the arena is significantly shrewd whereas the damage is more favoured. For example the infamous water meta team consisted of Mei, Mabui, 1010 GNW, Water Main, 40% nin and atk buff from barrier, 40% nin and atk buff from water main buff and lastly tentens crit buff so a total of 80% overall damage increase. Not forgetting the elemental weakness and strength there is just too much buff to the damage and if the damage proc's crititcal hit which explains why 1010 gnw's round one mystery hurts so much if you take it with no shields.

In terms of the defensive stance the only way to counter this is to get a line up that buffs resistance and defence. Ninjas like Hiruzen, Hokage Minato, Firemain shield buff, Earth main's defence knowledge buff. I also noticed that the shields are taking pure damage compared to the hp damage, the damage completely ignores all your defensive buffs if its your shield that is getting hit on the other hand if your HP gets hit your defensive buffs activates.

In conclusion, your only option in reducing damage taken is getting a defence and resistance buff and shields while your option in inflicting disgusting damage are Nin and atk buff, Barrier Buff, Crit proc, elemental strength against the weaker element, resistance and defence reduction skills. Now that there is the new jinjuriki ninjas that remove buffs and destroys barriers I think that the arena is getting a bit balanced.