So I made a homebrew Fighter subclass called the "Lionheart" but looking back on it I was unsatisfied with the end result. I still enjoyed the theme of subclass but the actual features felt very out of theme in hindsight. 

The subclass was inspired by the character Iskander aka Rider from Fate/Zero. He was larger than life man whose earnest behavior and frankly audacious personality won him the loyalty of his followers and even the respect of the self centered and arrogant Gilgamesh. There are also minor notes tajen from the Oath of Glory/Heroism Paladin but not a total ripoff (hopefully). 

I would like help workshoping and improving this homebrew to being more polished, all ideas are welcome so long as they are respectful.

"REVISED LIONHEART

Leaping into the fray with unmatched audacity and resolve, the archetypal Lionheart embodies the warrior spirit. Any fighter can be a charismatic leader, but what sets the Lionheart apart from others is their ability to transform their charismatic nature into tangible power in the form of a luminescent aura. With this aura, the Lionheart becomes an incredible boon for any military or party.

Enhanced Persona

When you choose this archetype at 3rd level you gain proficiency in Intimidation and Persuasion if you don't already have it. Your proficiency is doubled for any ability check that uses either of those proficiencies.

Leonine Presence

Starting at 3rd level your presence takes on a supernatural quality that you have learned to use to your advantage. You gain the following benefits:

• As a bonus action, you and up to three creatures of your choice within 10 feet of you gain temporary hit points equal to your Fighter level + your Charisma modifier. You can use this ability four times and regain all expended uses on after a short or long rest.
• Whenever you take the Attack action on your turn with a melee weapon, any hostile creature within 10 feet of you that can see you must make a Wisdom saving throw or be frightened until the end of their next turn. The DC is 8 + your proficiency modifier + your Charisma modifier.

Ferocious Strike

Starting at 7th level, you have learned to channel your aura in such a way that enhances your mobility and attacks. Your walking speed increases by 10 feet and the first creature you hit with a weapon attack takes extra damage equal to 1d4 + half your Fighter level.

Roar of Defiance

Beginning at 10th level, your resolve can rival even the most fearsome of creatures. As an action, you let out a bellowing roar fueled by your willpower. Pick any number of creatures equal to your Charisma modifier (including yourself) within 60 feet of you that can hear you. They gain advantage on any saving throws that causes a creature to be charmed or frightened for 1 minute. If a chosen creature is already under one of the effects mentioned, they instead remove that effect.

Once you use this feature, you can't use it again until you finish a short or long rest.

Unfallen

At 15th level, when you use your Second Wind feature you add +2 to your AC until the start of your next turn. In addition, you can use up to half your hit dice and add their roll to the total amount of health recovered.

Lionized

Beginning at 18th level, you become a rallying presence for your allies and a harbinger of death for your enemies. When you reach this level, your Leonine Presence extends to 30 feet and gain resistance to all non-magical damage."

This is an interesting subclass. The flavor is rich but there are some issues with wording and balance.

In Leonine Presence, being able to frighten enemies with every Attack action is way too powerful. Perhaps the temp HP and the fear effect share the same pool of limited uses and fear effect uses a bonus action? In the flavor text you mention a luminous aura, is this feature that? Perhaps you should glow for a short time after using it?

In Ferocious Strike, you write “...the first creature you hit with a weapon attack...” Does this refer to the first creature you hit per round, per combat, per day? If it’s per round, I worry this may be too much, maybe something like “If you hit the first creature you attack using the Attack action, you deal additional damage equal to half your Fighter level”. If it’s once per combat, I would specify it is once per combat.

Roar of Defiance, for 1 minute, gives allies advantage on saving throws against being charmed or frightened. The way it’s written it could be interpreted as they only get advantage on saving throws against only effects that would last for a minute. Perhaps the wording should be like this “for 1 minute, they gain advantage on any saving throws against being charmed or frightened for 1 minute. If a chosen creature is already under one of the effects mentioned, they instantly remove that effect.”

I would also add other conditions such as paralyzed and stunned. Both conditions that could remove a character from the fight just as frightened and charmed could.

In Unfallen, being able to roll half your hit die as a bonus action feels like a little too much. Maybe instead, once per long rest when you are reduced to 0 hit points, you can come back with one? When you use that feature, you gain some benefit like temp HP or a temporary bonus to attacks?

I’m a little confused about a line in Lionized. What do you mean by “gain resistance to all non-magical damage”? Who gains it? For how long? I would recommend no longer than 1 round.

Overall, extremely flavorful and well balanced for the most part. It shares some DNA with the Samurai and the Battle master but I think it’s very unique.

Yeah, astro basically covered all the issues that I was seeing too. I'll probably give more of an opinion and suggestions when or if you choose to show us an updated version.