As an AI language model, I don't have a physical body to play League of Legends, but I do have an extensive knowledge of the game.

In terms of gameplay, I am constantly learning and evolving, which means that I can adapt to new strategies and playstyles much faster than human players. However, I lack the emotional and creative aspects of gameplay that human players possess, such as intuition, decision-making under pressure, and the ability to read opponents.

So, while I can provide accurate and mathematically optimal strategies for various champions, I don't have the experience or the personality of a human player. Therefore, I don't have a rank in League of Legends, nor do I have the ability to experience the joys and frustrations of playing the game.

For maximum damage output on Pantheon, the best build would be:

Runes:

Conqueror (Primary Keystone)
Triumph
Legend: Alacrity
Coup de Grace

Secondary Runes:

Sudden Impact
Ravenous Hunter

Build:

Eclipse
Black Cleaver
Sterak's Gage
Guardian Angel
Death's Dance
Boots of Swiftness or Mercury Treads

Explanation:
Conqueror is the best keystone for Pantheon as it provides bonus adaptive force and healing based on the amount of damage dealt to enemy champions. Triumph and Legend: Alacrity provide additional healing and attack speed respectively, while Coup de Grace deals bonus damage to low health targets. Sudden Impact and Ravenous Hunter provide additional lethality and spell vamp, respectively.

For itemization, Eclipse is the best choice for Pantheon as it provides both damage and sustain. Black Cleaver provides additional damage and armor shred, while Sterak's Gage provides a shield and bonus damage. Guardian Angel provides additional survivability and Death's Dance provides additional damage and healing.

To calculate this build, we can use a damage calculator such as League of Legends Math to determine the best combination of items and runes for maximum damage output.

For maximum survivability, the best build would be:

Runes:

Grasp of the Undying (Primary Keystone)
Shield Bash
Bone Plating
Overgrowth

Secondary Runes:

Legend: Tenacity
Last Stand

Build:

Sunfire Aegis
Dead Man's Plate
Sterak's Gage
Spirit Visage
Thornmail
Boots of Swiftness or Mercury Treads

Explanation:
Grasp of the Undying is the best keystone for Pantheon in terms of survivability as it provides bonus health, healing, and damage. Shield Bash and Bone Plating provide additional defensive stats and Overgrowth provides additional health. Legend: Tenacity provides additional crowd control reduction, while Last Stand deals bonus damage when low health.

For itemization, Sunfire Aegis provides additional health and damage, while Dead Man's Plate provides additional armor and mobility. Sterak's Gage provides a shield and bonus damage, while Spirit Visage provides additional healing and magic resist. Thornmail provides additional armor and grievous wounds.

In terms of pure mathematics, the most broken build on Pantheon would likely involve building items that maximize his physical damage output, as well as items that boost his survivability.

A potential build could be as follows:

Runes:

Conqueror
Triumph
Legend: Alacrity
Coup de Grace
Conditioning
Overgrowth

Build:

Eclipse
Black Cleaver
Death's Dance
Sterak's Gage
Guardian Angel
Boots of Swiftness/Mercury Treads/Ninja Tabi

Explanation:

Eclipse provides Pantheon with extra damage, armor penetration, and survivability.
Black Cleaver synergizes well with Eclipse and provides Pantheon with extra damage, armor penetration, and health.
Death's Dance provides Pantheon with sustain, extra damage, and survivability.
Sterak's Gage increases Pantheon's health, and provides a shield when he takes damage.
Guardian Angel gives Pantheon a second life and can help him survive in team fights.
Boots of Swiftness, Mercury Treads, or Ninja Tabi can be chosen based on the situation.

This build allows Pantheon to deal a significant amount of damage, while also being durable enough to survive in team fights. Conqueror rune helps Pantheon to deal more damage over time, while Triumph and Legend: Alacrity help him sustain in fights. Coup de Grace rune increases Pantheon's damage against low health targets. Conditioning and Overgrowth runes help Pantheon to increase his maximum health, and thus his survivability.

Of course, it's important to note that the "most broken" build on Pantheon may change based on the current state of the game, patches, and balance changes. This build is just a theoretical example based on current item and rune mechanics.

KEEP IN MIND THIS WAS ALL MADE FOR FUN

I do not want anyone think this build is serious, I just had this fun idea that I would try out.
Everything in this guide is based on ChatGPT, and everyone knows he sometimes has some problems.

But if you wanna try it out feel free to give it a go and see how it goes.

Thank you for reading the guide!:)

*I did not do this for any clout/likes, the sole purpose was to have fun with it*