Fleeting Expertise is at 4/5 because you've already hit the efficiency cap.

Build Attributes

• Maximum efficiency and duration for extended survival/solo missions while invisible
• Support role with cheap, high-duration arrows for teammate invisibility, covering revives, or sleeping key enemies
• Maximum duration on sleep arrows without reducing area of effect
• Maximum efficiency for arrow & [Artemis Bow] spam

Operator Tree

If you have Zenruik tree on your operator with Energy Pulse, you will never run out of energy. When low, throw a invisibility arrow down, even [Energy Siphon] alone will [Regen] more energy than you lose from the arrow's duration. With Energy Pulse you have infinite energy & thus infinite invisibility.

Weapons

Combined with a dagger & [Covert Lethality], this build possesses infinite scaling for survival mission endurance. If you want even more energy, use a the Rakta Dark Dagger with Gleaming Blight. Radiation proc of the Rakta Dark Dagger is not a problem since you'll be 1-hitting enemies with [Covert Lethality], preventing you from getting caught in confused enemy fire.

Arcanes

These don't really matter, pick what you want. I liked the synergy these two brought to the table, so I opted for them.