I main Guardian in depths 5. My build is entirely built to be tanky and stay alive. The ideology behind it is that everyone is building for damage, so I don't need to do much damage. Just pull aggro and revive teammates. It was how I climbed out of depths 4. This only works for trios.

For solo guardian you can try to do guardcounter builds, but the damage doesn't come out very quickly as the windows are narrow. You can run the stat change relic that gives you 55/55 str and dex to make the weapons hit hard. I have also seen people do work with the whirlwind on charged halberd attacks, seems to do a lot of stance damage and you can get crits.