Thinking on it, maybe it should be the cenobite who gets the armed flurry, not the Martial Artist? Martial Artist can certainly afford to lose it, whilst Cenobytes would benefit the most from having an armed flurry - possibly not even restricted to monk-only weapons as opposed to weapons they're proficient with.

Gladiator Level 6.

Full simple weapon proficiency, full martial weapon proficiency, and three exotic weapon proficiencies.
Light and Medium armour proficiency.
Shields (not specified to include Tower Shields).
Three flexible Fighter Feats.
Counts as a Level 6 Fighter (Meaning, I believe, Weapon Specialisation and not much else).
May reroll a single miss per encounter, cannot be disarmed, and weapon cannot be sundered (as ever, absolute immunity seems a little excessive, perhaps they could get a +Class Level as a bonus to resist sunder and disarm attempts with it?)
Modified Whirlwind attack, essentially targeting between two and three targets at full BAB.
May move 5' as a swift action.
May take 10' steps instead of 5' steps.

+6/+1 Attacks
+5/+2/+2 Saves
15-60 + Con HP
4 + Int Maxed skills.

Once per encounter:
Remove all non-lethal damage and a slew of effects, not including most mental ones.
Additional Full Attack as a swift action. The RAW does not grant an additional 5' step, so that's fine.
Ignore any one attack as an immediate action.


Overall, the base chassis gives a lot less than the Brawler, who basically uses a Bastard Sword in each hand when they're level 6, attacks more often, has better saves, and with a Chain Shirt and 14 Int or Wis is getting AC equal to full plate (half of which applies to touch attacks). Has Evasion, moves faster, has Standard Action full attacks... And unarmed strikes can't be disarmed or sundered.

If it's the Battlefist, then they're even potentially doing Greatsword Strength-and-a-half damage. With reach.

And I almost forgot, they have pounce by default.

With this in mind, it may actually be fairer to make the Brawler medium BAB. It shouldn't greatly diminish the class, and will rein it in here. They'll still handily fulfil the mobile combatant archetype.

Anyway, on to the archetypes.

Brute:
Needs an "if positive" condition applied to Constitution modifer DR.

Rage 3x a day. "As a Barbarian of his class level" is slightly awkward, as a literal reading means that he may earn an additional Rage/day at level 4, but still gets the basic +4 Str/+4 Con/-2 AC and +2 Morale bonus to will saves.
Strength to Intimidate.
40' base speed, not slowed by wearing Medium armour.
May charge over difficult terrain and change direction up to 90 degrees whilst charging.
Pounce, and charge does not give an AC penalty.
DR of at least 2 + base con modifier/- whilst raging.
+6 untyped(?) bonus to Will saves against hostile mind-affecting effects whilst raging. Presumably stacks for a +10 Will save.

Not a big fan of rage, but it's a solid archetype, at least whilst raging. I'd even consider giving it an extra rage at level 6 as a minor boost.

Kensei:

I won't go into the homebrew disciplines for fear of what I'll find.
6 Manoeuvres known.
4 Manoeuvres readied. Recovered with a swift action.
2 Stances known.
Largely irrelevant "WoC is always discipline weapon", but opens the potential for Shadow Blade Dex SAD with a few feats.... With an Elven Courtblade.
Immune to fear.
Maximises damage on successful crits, if the threat was from a natural 20.

I would be concerned that he was a little lackluster on the archetype traits, but manoeuvres make up all of that. This is pretty well balanced in my opinion.

Master-At-Arms

Ignore metal-based DR.
Switch WoC as a swift action.
Basically free +4 to what I assume to be: Bullrush, Trip, Disarm, Feint, Sunder, Overrun, or Grapple. (I'm not sure if "Combat Manoeuvres" is a game term in D&D, but I think that's what it is in Pathfinder).
WoC is Keen and gets an extra x1 to its multiplier.

Subtle but potent, with his WoC (which is obviously pretty much always) he has the good half of every "Improved X" feat and is set up for easy specialisation into all of them. A Fullblade with a 17-20/x3 2D8 (with which they are proficient as one of their free proficiencies) or a 19-20/x4 Dwarven War Axe in each hand are both serious damage dealing options.

Pit Fighter
It should possibly change "connects" to "hits" with an AoO, I'm not sure if connecting is game terminology.

Needs the Combat Reflexes feat harder than the Druid needs Natural Spell.

Take a 5' step every time an AoO hits.
Gives mages serious issues with Defensive Casting and keeping spells.
Full Attacks on every AoO.

AoO specialist, if it weren't for that awesome capstone I'd consider it a rather modest class after removing those more insane features.

For optimisation...
With Karmic Strike this guy gets to Full Attack anyone who hits him in melee.
With Hold the Line he gets to Full Attack anyone who charges him.
With Close Quarters Fighting he gets to Full Attack the Breathstealer (or anyone else) whenever he attempts to pull grapple shenanigans, and add the damage dealt as a bonus to resisting the grapple.
With Expert Tactician, if you hit with your first AoO of your Full Attack, you get an immediate +2 to hit with the second, and for the next round.

He basically gets the Double Hit feat for free if he TWFs.

For survival purposes, it's arguably worthwhile to drop two feats to pick up Stone Power for temporary hitpoints each round, or the Fey Heritage feats for DR 4/Cold Iron, since you'd be getting hit a lot, and Karmic doesn't care if you get hurt or not.

Vindicator:

Skipped since he's getting potentially reworked. Conditional bonii aren't great, compared to the other archetypes he's a bit left out.