Alright, so I pestered Deathmax some and he gave me access to the raw data for summoner's arc. I've been working on interpretting it for the last couple hours and have finished checking on all of the EX skill data.

Feel free to reference /u/FNMokou's post on this yesterday for acquisition methods.

You'll notice some unused skills in here. They're present in the data, but aren't used anywhere. I've listed them under the weapon they seem to be attached to, but none of them seem to be worth having, so we're not missing out.

Brave Sword

• Level 5 - Brave Sword's Courage

  • 30% BB ATK, 3 BC/turn

• Level 40 - Brave Spirit

  • 60% BB ATK, 1 BC when attacked

• Level ? - Formidable Spirit

  • 1 BC when attacked (50% Chance)
  • Unused Skill?

Brave Spear

• Level 5 - Brave Spear's Protection

  • 10% HP, 500 10% REC HoT

• Level 40 - Proud Knight

  • 20% HP/DEF, 15% Mitigation (10% chance)

• Level ? - Master of Evasion

  • 10% Mitigation (20% chance)
  • Unused Skill?

Great War Axe

• Level 15 - Art of Demolition

  • 20% ATK, 10% Crit Chance

• Level 40 - Ferocious Anger

  • 30 ATK, 4 BC on Crit

• Level ? - Stark Lightning Strike

  • 20% Spark Damage
  • Unused Skill?

Twin Pistols

• Level 15 - Holy Bullet Shot

  • 50% Spark Damage, 10% BC/HC Drop Rate

• Level 40 - Double Shot

  • 50% Spark Damage, 1-3 BC on Spark (50% chance)

Great Sword

• Level 15 - Shining Knight's Armor

  • 15% HP/ATK/DEF

• Level 40 - Imperial Barrier

  • 25% HP/DEF, 10% Guard Mitigation

Yearning Scythe

• Level 15 - Demonic Healing Blood

  • 20% ATK/REC, 10-15% Heal when Attacked (20% Chance)

• Level 40 - Crimson Butterflies

  • 30% HP, 3-5% Lifesteal (10% chance)

Star Bow

• Level 30 - Arching Border

  • 20% HP/DEF, 15% Injury/Weak/Sick, 10% Paralysis/Curse/Poison

• Level 45 - (Level 45 Skill)

  • 30% HP/ATK, 80% ATK vs ailments

Falcon Blades

• Level 30 - Elegant Flash

  • 1 Hit Count, 100-120 Heal on Spark

• Level 50 - (Level 50 Skill)

  • 35% ATK, 50% Spark Damage

Dark Blossom

• Level 30 - Obscure Practice
  • 75% ATK when BB Gauge is Full, 20% BB Cost Reduction
• Level 50 - (Level 50 Skill)
  • 0-40% ATK/DEF/REC based on HP remaining, 50% BB ATK

Twin Daggers

• Level 25 - (Level 25 Skill)

  • 3 BC/turn, 20% BC/HC drop rate, 4% Item drop rate, 20% Zel drop rate, 15% Karma drop rate

• Level 40 - (Level 40 Skill)

  • 20% HP/ATK/DEF/REC

Hammer

• Level 30 - (Level 30 Skill)

  • 50% Crit Damage, 1-2 BC on Spark

• Level 40 - (Level 50 Skill)

  • 35% HP, 50% ATK when HP > 50%

Protagonist Sword

• Level 50 - (Level 50 Skill)
  • 10% HP/ATK/DEF/REC, Add 6 BC/turn BB Regen for 3 turns to BB/SBB

Savage Whip

• Level 10 - Sharp Ingenuity

  • 20% HP/ATK, 30% BC Fill Rate

• Level 30 - Swirling Dance

  • 20% ATK/DEF, 50% chance AoE normals (no penalty?)

Crystal Staff

• Level 25 - (Level 25 Skill)

  • 25% HP/DEF/REC, EWD Null

• Level 50 - (Level 50 Skill)

  • Add Ailment Cleanse to BB/SBB

Claws

• Level 15 - Hurricane's Wolf Soul

  • 1 Hit Count

• Level 40 - Wolf's Awakening

  • 15% HP/ATK/DEF/REC, 10% BC/HC Drop Rate

• Level ? - Wolf's Intuition

  • 5% Zel Drop Rate, 2% Karma Drop Rate, 1% Item Drop Rate
  • Unused Skill?