Two tiers above one of you, actually. Gregor and Evvie were both tier 4. 

As for why you lost, it was a combination of Arthur's abilities and a lack of teamwork/adaptation. Evvie had armor that could resist his electricity, was immune to Gregor's attacks, and strong enough to at least temporarily restrain Arthur. Gregor had fire attacks hot enough to hurt him, and Adrian (or gregor, or evvie) could easily have removed all the water from the plateau to limit his electrical abilities. You had the tools you needed to win.

As for the strength of Skall's character, that's not the part I take issue with. I would happily send Krix out to face a demigod that can lift 100 tons and is impervious to modern firearms. It's the fact that this extremely physically potent demigod can also turn intangible at will and become immune to any attack used against him (as well as potentially copy those attacks), AND heal back from any wound you might manage to inflict in mere moments that makes me hesitant to simply remain silent and let the chips fall where they may. If it was just the healing, durability, and strength I would see no issue.