vMA - StamNB Help

Alright so for most of the afternoon I've been on vMA however for some reason I cannot defeat the first boss.

I just don't know what's going wrong. I've tried multiple ways: ignoring the adds, focusing on the adds, getting all sigils at the start, using (once I've actually found) them as needed.

Current bar setups:
2H: Surprise Attack, CamoH, Reverse Slice, Rally and Vigor. Ultimate: Flawless Dawnbreaker.
Bow: Scorched, Double Take (to reduce stamina cost from using Shuffle), Razor Caltrops, Relentless Focus and Siphoning Attacks. Ultimate: Veil of Blades or Meteor.

I'm currently using Serpent Mundus, blue v15 stam and health food (tried the Orsinium stam stuff but that wasn't any better) and my PvP tripots of stamina, immovable and crit.

v16 gold (except bow) 5x HRage and 3x NMGaze gear (stam enchants) and 3x Agility jewellery (2x robust w, damage & 1x healthy w, recovery)

CP: 301
Mooncalf = 95
Warlord = 5
Mighty = 74
Thaumaturge = 25
Precise = 1
Hardy = 49
Elemental = 49
Thick Skinned = 2
Bastion = 1

Buffed stats (incl. food and potions)
Health = 19k
Stamina = 34k
Stam. Recovery = 2k
Damage = 3.5k
Crit = 62%
Resistance = 11k each

Is this purely just a L2P issue or is there something I'm missing?