

I think giving the Kensai a single weapon proficiency or limiting the ability to use Kensei powers with a single type of weapon is a blunder.
I would prefer something similar to requiring something similar to an Eldritch Blade's weapon bond instead: you can bond with one weapon per short rest and your Kensei abilities key off of that bonded weapon.
Because there are many times you can't avoid staying out of melee - sneak attacks, opponents with movement, close quarters, hoards, moving in to take an action, etc.In this case, consider- why not take a bow and then just never get into melee?
Dual wielding daggers or hand axes do less damage than one long sword used 2-handed.Or take a weapon you can use in melee or at range (e.g. hand axe) and then dual wield?
He likely carries more than one. And can make his own at 3rd level.What if this guy loses his only weapon before 10th level?
Except it says he "rejects armor" so no armor or shields; there is no shield feat anyway.The other arguable balance point is the no armor proficiency- which is pretty easy to get around with feats, or with training (if the DM allows armor proficiency to be earned via training), or magic items, or a friendly spellcaster.
That's not the intent of the maximum damage. That is my fault for writing it ambiguously.The maximum damage thing- starting at first level, no less!- is also pretty overpowered, in my opinion. You're essentially giving a great weapon fighter maximum damage on every hit until 5th level. Holy crap.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.