A Rebuke is stronger than a Goliath vs lightly armored/already shredded targets.
The solution is to combine a Rebuke with others sources of shred in the team (a Goliath, a Fury, hand grenades, Armor Break and later in the game there are even more options). A Rebuke has max range of all fire weapons (with the exception of Armadillo's Purgatory GL).
I rarely play with Impossible Weapons because I like to rush the game and they come too late and more importantly on Etermes the amount of ancient resources is set to 50%.
BTW, did you know that there is an option on starting a new game named “Adjust Impossible Weapons“. You can revert them back to Vanilla stats and functionality.

is that only on starting a new game? I can't do it mid-campaign?

AFAIK, yes.

Ragnarok buffed in mod as solid late-game Goliath "upgrade"

Yea, the Ragnarok is the most powerful item in the game.... The rockets cost A LOT. Rightfully so.

An Archangel Rocket Launcher isn’t bad either and comes earlier although expensive, too: one-shots a Siren’s head to break mind control, two-shots an Explosive Bomb Chiron’s abdomen (3 shots required on Etermes), …

Heavies FTW.

I suppose Archangel could be a viable 3rd weapon in the quickslots... Deceptor. Goliath. Archangel situationally

Yes, I use it situationally. But then it is a game changer.

It one-shots arms on human enemies across the map with its accuracy. Very useful in ambushes. Screw the Heavies (with Grom AC) and Snipers.

I've confirmed that the Archangel is useless.

I shot an unarmored Scylla head with it.. You know what the Archangel did? It caused 80 damage to the head... That is less than useless

It takes like 3 or four missiles to destroy an arthron shield. It's a total waste of a weapon slot

Archangel does x3 damage to the body part HP. So it will 80 dmg to global HP, and 240 to the body part HP. Also, it has 50 pierce, so no need to shred the body part first.

Arthron shields aren’t body parts. You should target the arm where the shield is attached.
Archangel vs Scylla head: what did you expect? There isn’t a single weapon in the game to one-shot a Scylla head.

Not expecting to one shot it.. But I did want to damage toward disabling the head so it wouldnt keep using its sonic head to daze my guys. Even so, I'd still have to hit the Scylla head like 4-5 times with an Archangel missile

It's useless against Tritons, since disabling an arm won't stop it from using its gun.
Also, you cant even destroy the gun the Triton is holding.

Given all these limitations, I'd much rather use a Deceptor, Goliath, and Flamethrower in my quick slots...It's beneficial to have one weapon the heavy can use that only costs 2 AP and the Archangel is a waste at 3 AP.. And the flamethrower does heavy damage on Tritons

Re Archangel: usually I don’t use it against Tritons. But in one final mission on Etermes I destroyed 2 Triton Sniper Rifles with 2 Jet Jump + Onslaught + Archangel Rocket shot combos.
What is your preferred approach to disable a Scylla Sonic Head? IIRC it’s something like 750 HP. Yes 4 Archangel Rocket Shots (=12 AP or 8 AP if Boom Blasted or Quick Aimed) are needed but the accuracy is pin point (IIRC effective range of Archangel is 400). Sniper Rifle? That would be 6 shots (=18 AP) with a Cyclops and 7 with a Pythagoras with worse accuracy. Assault Rifle at medium range would be 4 EDIT: 5 shots (IF all bullets hit). Shotgun or Machine Gun at close range? I don’t want a fully operational Scylla that close.
If you don’t like Archangel then don’t use it. It may be useless to you but not to others.