Spectral blade arena BiS

If everything rolled perfectly of course.

WHY PERKS?
Combo attack is just free damage for your attacks, it can be up to an extra 5-10 weapon damage added to your already high numbers

Barricade works while guarding with Pavise, blade and bare handed so free damage resistances.

Sword mastery obviously for the blade, free action speed, damage and movement.

Swift for mobility but you can swap for counter attack if you want, but IMO counter attack overrated for longsword fighter. It's also very reliant on you getting a successful parry. Mobility is more important in arena to gap close.

Pavise or crossbow, you can bring both for arena. Pavise to gap close against rangers/casters. Crossbow to shoot from far. Debuff durating on it for wizards/warlocks DoT and ranger feet shooting. Magic resist obviously for wizards AoE fireballs and lighting strikes. Projectile for rangers.

WHY SKILLS?
Adrenaline rush can be swapped for swift since swift is very strong right now to gap close but I prefer adrenaline to box out other melees. 15% action speed + 5% sword mastery AS + 5% spectral blade AS + whatever AS you have is A LOT, also lets you not have to focus alot on action speed or dex on your gear.

Spell reflection is IMO underrated. Everyone thinks you have to run it with just a shield but you can actually use it with a longsword. Many times I've deflected spells while holding a LS. For some reason spectral blade doesn't have the glowing blue effect (unless they patched it). Also since Wizards are strong right now in arena, the 15% extra Magic resist helps a ton and stacks well with barricade. 75 flat MR + 15% magic resist and whatever your gear is.

WHY GEAR?

Of course this is insane BiS crafted gear which is very hard to achieve. You can run nearly the same as their non-crafted counter parts and still achieve good numbers. However certain pieces are a must such as Buckled Boots, Spectral cloak, and necklace of peace. Flat HP is king right now since HP modifiers were removed a long time ago and any HP is good for fighting. Dark Plate armor is the best chest piece because of pretty high armor rating and built in magic resist. Plate Curiass doesn't have any magic resist built in. 50% PDR is pretty good IMO, everyone in arena is stacking armor pen anyways so I don't think having to reach max is a must.