As of recently, Garry was at the pinnacle of his life! He became an Arch Mage at a fairly young age, young for a demonic basilisk, at least, and ever since he got to this rank, he had eased up on a lot of his beliefs or principles, and was just enjoying his life.
In hindsight, he didn’t care much to progress into the following rank, which was that of an Arch Magus. He figured that such a title was years away from him, if not decades, so he simply didn't think about it much. He wasn't worried that he stumbled into another mana bracket as soon as got to the third level of the seventh realm of mana. He was okay with it.
Initially, one of the main reasons he chose to stay in this universe rather than going back to the universe of hell, was because he wanted to help Timothy, his former summoning master, progress. He felt indebted to help Timothy, because he had saved him from deadly wounds back in those old ruins, so he chose to stay.