Trinity’s niche would be as a support frame, most effective in endurance missions like Survival and Defense. To a lesser degree, Trinity is also useful for Eidolon hunting and isn’t a bad choice if you’re playing public and trying to learn how to do these bounties.

While her general kit may be a little dated with the shift to Shield Gating, her abilities are still very useful for defending objectives and for providing your team with damage reduction. I think her main weakness is just how short her ability duration is for her 1st, 3rd and 4th abilities.

Well of Life:

• This is probably Trinity’s weakest ability, essentially turning an enemy into a healing mote similar to Garuda’s Blood Altar/Wisp’s Health Mote, while also granting Status Immunity to allies within the Well’s radius.
• My main uses for Well of Life are for to build Combo/Maintain for either melee weapons or snipers. Headshot gimmicks like Death Knell can also be proced on a Well of Life enemy. In a more recent update, Well of Life also gained the ability to protect allies from Status Ailments, my main use case for this is preventing Rad procs in defense-based sortie missions.

Energy Vampire:

• This ability deals True Damage, bypassing shields and armor, pairing well with Viral and actually benefits from having low duration.
• With the Vampiric Leech augment, this ability is easily able to replenish shields.
• Trinity built around Vampiric Leech has become my preferred Index build because of its good survivability, energy management and single target damage. The downside to focusing on Energy Vampire’s single target damage is that Trinity’s other abilities are heavily impacted by modding for negative duration.

Link:

• Transfers damage and Status to any enemies linked to Trinity.
• Provides 75% damage reduction.
• While not useful for fighting most Corups, the Abating Link augment is very useful for quickly stripping armor on linked enemies.
• Because this ability gives Trinity Status Immunity as long as it links to an enemy, I find it very helpful in Sorties with Radiation/Magnetic modifiers.

Blessing:

• Both heals and restores shields.
• Also provides 75% damage reduction to all allies within affinity range and is capped at 50% damage reduction for objectives.
• I find the Champion’s Blessing too annoying to maintain because of the short duration and often hard to actually find something that needs to be healed to get the buff in the first place because of shield gating/Overguard. You can get around Shield Gating by healing a specter without shields like a Nidus Specter or Ancient Healer/Combat Discipline if you really wanted to use this augment, but Overguard will prevent you from taking health damage making healing a specter the only reliable way to get the buff (as far as I can tell, a specter can’t be buffed with Overguard).