Disclaimer: This is a work-in-progress build

Build Description:
[Banshee] is a very squishy frame and most of her survivability comes from her cc and utility abilities, which isn't great. While there are a lot of builds that focus on that aspect of her kit, namely using gloom, I personally am not a big fan of this kind of playstyle (ie. either slowing and ccing enemies, which isn't effective on overguard units, or needing to shield gate every few seconds and constantly needing to zip around and damage enemies just to even survive). Thus, I have decided to make this [Banshee] build for Steel Path missions. With this build, [Banshee] becomes a pocket [Trinity], supplying both energy and health to allies and herself while still maintaining her destructive capabilities with an armor-stripping Sonic Boom and a damage-multiplying Sonar. An umbral forma is unfortunately necessary.

[Banshee] is normally way too squishy to make use of [Adaptation] and other such defensive mods, however, with all three umbral mods, we can increase her health up to 1070. We also run 5 blue archon shards, giving us at least 150 armor each for a total of 750 extra armor (tauforged if possible, but regular is also fine while you work up to them). Armor archon shards are incredibly important as they are our first line of defense, along with our health. We also slot [Adaptation] for 90% resistance to damage types as we can actually make use of this mod now with our current health and armor. We are keeping [Adaptation] at rank 10 because it barely affects our build and because there's not enough space unless we spend another forma. Arcane [Guardian] for even more armor totaling 1806 armor. Molt Reconstruct because it immediately gives you and your squadmates a large amount of health. Other alternatives are Arcane Blessing, Arcane Grace, or literally any other Arcane you'd rather slot, but Molt Reconstruct is probably the best option. The last part of the equation is [Hunter Adrenaline] + [Quick Thinking] + [Primed Flow]. With these three mods, you will have a huge health buffer. 744 max energy will make [Banshee] tough to kill with [Quick Thinking] and [Hunter Adrenaline]. On top of all this, silence is still a great ability that ccs enemies and silences both acolyte and eximus abilities.

With the umbral mods, we are also at 177% ability strength with Sonic Boom stripping 100% of armor and sonar providing a high 8.8x damage multiplier to highlighted body parts. [Umbral Fiber] is intended to be rank 0 as [Banshee Prime] has barely any base armor to use that mod effectively. We are mostly using it for the set bonus.

Helminth
Voracious metastasis is my helminth of choice here. It provides us with 850 health over 10s with our build, and it also supplies teammates with 50 energy per cast. Additionally, since we have Molt Reconstruct, we will restore also restore an additional 300 health to both ourselves and our allies. [Brief Respite] Is our aura mod, and each cast will max out our shields with a decaying dragon key, making [Banshee] harder to kill than she already is. Voracious metastasis then is our main source of healing and support, but it also functions as our panic button. You can choose whichever other helminth you'd rather take if you really want to but I would at highly recommend that you at least pick one that regenerates health like Well of Life or Blood Alter because Molt Reconstruct is not enough. Molt with [Regenerative Molt] is also a decent choice as it draws aggro, cleanses status effects, gives you a speed boost, regenerates health, and also has no casting animation. However, there's not enough space in the build to fit the augment unless we remove Sonic Fracture, our armor-stripping augment.

TL;DR
Banshee Prime is essentially now a tank pocket trinity with Sonar and armor-stripping capabilities while replenishing energy and health to both herself and her teammates. Viable in base steel path. You can use any weapon of your choice and aren't locked to having specific loadouts.

Voracious Metastasis with Molt Reconstruct gives squadmates energy and health (we only benefit from the health), and with [Brief Respite] and a decaying dragon key, it also brings our shields back to [Full Capacity].

[Primed Flow] + [Quick Thinking] + [Hunter Adrenaline] helps [Banshee] survive even when she dips below 2 hp.

Archon Shards, [Adaptation], umbral mods, and arcane [Guardian] greatly boost [Banshee]'s defensive capabilities.

Checklist
1. Blue armor archon shards x5
2. Molt Reconstruct R5
3. Arcane [Guardian] R5
4. 1070 health from 3 umbral mods
5. [Adaptation]
6. [Primed Flow] + [Quick Thinking] + [Hunter Adrenaline]
7. Voracious Metastasis
8. [Brief Respite] Shield Gating
9. Silence

I welcome any feedback to make this build better