Do not rush the objective when there is a deadzone placed. This means playing passively and prioritising targets on the enemy team while waiting for the deadzone to disappear. Once it's gone, the team can group up and start to slowly cap the point.
As a support, be wary of Dead Zone! Do not stand inside it unless it's unavoidable and do not attempt to use healing abilities on allies affected by it until they've been cleansed. Remember that the effect lasts for 2 seconds after exiting.