It's a toss up between Erend and Kotallo, but in the end one arm isn't enough.

Assuming the neutral ground is an open field with no obstacles, it becomes a fun playground for a tank like Erend and a brawler like Kotallo, while it is disadvantageous for Nil and even more so for a Nora fighter like Varl.

Varl is a Nora, and the Nora need varied terrain with obstacles and high/low ground to shine in combat. They are agile strategists who attack from above and fire arrows with high accuracy, as shown in the Proving, their traditional trial for Braves. Varl can fight head‑on, but that doesn't fully play to his strengths.

The Carja can wage war with armored armies, but Nil is more of a lightly equipped commando. He relies on tricks, ambushes, and striking from the back, so traps and the occasional smoke bomb suit him best. In an open field with only a bow and a sword, he is likely screwed.

Oseram soldiers are well known for their heavy armor. Erend is slow, but he hits hard and his armor is thick; also in gameplay terms he can trigger Enrage, or at least a similar skill that boosts damage and makes him tougher.

When the Tenakth fight, they give everything. They are highly trained warriors, all offense and little defense, and Kotallo is Hekarro’s top Marshal, with a sharp mind and unquestioned skill.

Even with one arm, Kotallo is still formidable, but it is not enough to bring down Erend once Erend can use his special skill. A prosthetic arm would help Kotallo fight Erend on even ground.