War is truly a problem in 1vs1,
usually when I had to face one of them regardless of my job I try to make his Berserk wear off running/hiding/CC.
As MNK ... in that little arena... mh I dont' know if Steel peak + Fist of wind when he pop could save you.

as melee also ou have to manage your burst too, NEVER burst if he has PushBack / Vengeance up.
If he pop both of them and BloodBath it's not even a fight, it's just a suicide XD

Just random hints, I'm neither a WAR nor a MNK
Ah you have a pacification, you can use it too to negate his burst.