Atlas practically vanished the moment they revealed their hostility.
He had many things in his arsenal at the moment, but he couldn't be called versatile. All of his moves served relatively the same purpose.
Exploding Runes, Flame Thunder, and Flame Wheel were all damage moves that could be used at range. When he was in close combat, Atlas usually used pure qi without charging his fists with his element.
He had an arsenal hidden in his mind, but currently, he only had the power for those three moves. Supported by Burst Steps and his weapons, he was able to do fine with these as the core of his fighting strategy.
However, given that the entire group in front of him was made up of Earth Sages, he couldn't just "do fine."
He vanished from their eyes due to some trickery. The mask he was wearing now, the mask he put on before entering this trial, was imbued with an effect that allowed him to temporarily turn himself invisible.