It's simple: 90% of the time, you're fighting in melee combat. I use either [Skana] or [Nikana] for that, and Gloom for healing. If I need to shoot someone, I use [Lato] or [Braton]. The ultimate ability is only used for stripping armor (it's not always worth it, it's easier to just take down the enemy in melee combat), you can completely do without Umbra Forma.
5 Tauforged Violet Archon Shard all Gain +25% (+37.5%) Melee Critical Damage. When max Energy is over 500, the damage boost doubles.