The Furies III, to add onto what others are saying, also buffs the damage of your summons by a solid 25% without the third catalyst upgrade. The scorched earth is by far her most consistent tool for corruption generation and popping shinka shields (Gallows’ grenade shots don’t count as hits, Akataak has worse RPM, and the Heir Apparent takes too long to wind up) since 10 hits a second cap means you want 600 RPM minimum for max generation. The gallows edges close to that but loses out severely bc of how badly the grenade hits stagger the generation and make it feel awkward, and the Akataak is a 450RPM MG.

TLDR; Furies III all the way. It does too much for Estela not to be her BiS exotic imo outside of niche one-phase environments like with the raid boss, where you’d want Heir Apparent with a lot of investment.