There are various other systems to increase your character's damage abilities outside of Equipment.
The legendary accessory augment system allows you to tackle specific Hard Mode dungeons for a chance at Psyche items, which will allow you to further increase your legendary accessory power. Each dungeon has its own unique Psyche related to the augment system, in addition to the Battlefield Traders having their own PvP-focused versions.
Unity, an account-wide Rank system opened by pressing CTRL+H, will increase all of your character's attributes. After starting at Rank 1, each Rank will earn you special benefits such as HP, Defense, and Critical Rate. You can increase your Rank up to Rank 180. To increase your Rank, you must gain Reputation.
The Compound system, accessible by pressing SHIFT + P, is a new enhancement system designed to help boost your character’s base stats by adding unused accessories and fusing them with Runes.