My setup for context: Operator: Magus Anomaly & Magus Lockdown Amp: Eternal Eradicate & Eternal Logistics.
Anomaly and Lockdown give light grouping and CC to all frames, at all times, regardless of energy constraints. They open the game up in a completely different way and I don’t think I will ever switch off of them with the exception of Magus Elevate for things like eidolon hunts and profit taker where CC is irrelevant.
The Eternal combo gives you more than enough damage to kill things, and unlike a lot of the old arcanes they’re not percentage based activations. Dump your energy bar, get a huge power spike on demand, always when you want it, always within your control. Combined with Unairu or Madurai, even with Zenurik’s AoE slow to a point, that’s more than enough damage to take out enemies even well into the steel path. If you’re running armor strip or unairu then you will always be able to kill with the operator.
Magus Melt is unique among the operator damage arcanes. Things like Virtuos Trojan and Forge convert damage into their respective types. Magus Melt works like a heat mod for your arcanes, giving you additional bonus damage on top of your void damage, without taking anything away. It’s viable because of that, but I just don’t find I need that level of firepower enough to give up Anomaly and Lockdown.
x77 isn’t really “required”, it’s nice for Eidolon hunts because the propa scaffold can be timed to consistently one shot eidolon shields especially now that we have Eternal Logistics and Eternal Onslaught, so you’re not relying on RNG procs anymore.
I run a 747 as my “daily driver” and it doesn’t steer me wrong, though I’m considering making maybe a 147 for Duviri Circuit specifically. The Phad scaffold, x4x, is one of the best generic mook clearing amps out there. Great ammo economy, good damage, especially if it procs Void and gets a mini magnetize effect.