Oh! I might simplify the restrictions to “must only be wielding one handed weapons that are light, finesse, or defensive, and be wearing no, light, or medium, armor.”
It’s a fast, precise, and agile charge.
And I’ll go ahead and change the damage bonus to speed, to make it more feel like an especially fast charge. I also realized that I didn’t write up charge attack quite right, it is meant to give extra movement while restricting you freedom of movement. Perhaps it gives opportunity attacks advantage against you, as well, mean flèche neutralizes a downside rather than being a “big” bonus with its giving disad.
So,
Master Duelist
You are a master of personal combat with light and defensive weapons, whether skillfully deflecting attacks in a sudden defensive stance, using an enemy’s misstep against them, or swiftly and nimbly charging at a foe to throw them off balance.
You gain 2 manuevers dice, which can be used to power the manuevers listed below, or any other manuever you know.
Flèche
Light Fighting
When you make a charge attack, opportunity attacks against you have disadvantage, and you can spend a maneuver die to gain a bonus to your movement equal to 5 times the result of your maneuver die roll, and when you attack the target you can treat a die result of 18 or higher as a natural 20.
Parry
light fighting
As a reaction when targeted by an attack, you can grant yourself a bonus to AC equal to your proficiency bonus that lasts until the start of your next turn.
Riposte
light fighter
When a melee attack against you misses, you can spend a maneuver die to grant yourself a bonus action attack that you can take on your turn against the attacker, with a damage bonus equal to the result of your manuever die.
————
Okay, I made the parry just be the existing defensive duelist but last until the start of your next turn, and the riposte uses your bonus action on your next turn.
Flèche has a fairly small bonus at-will, but the speed buff and crit buff require spending the maneuver die.
The light fighting tag means that you must be using only light armor, medium armor, or no armor, and weilding only one-handed weapons or double sided weapons which are light, finesse, or defensive. (Might drop the double weapons but it feels right to have them be treated like two weapons for stuff like this)
The only thing I’m dissatisfied with for duelists still is that there no reason to not have something in your off-hand.
My other concern is that maneuver dice currently come back with a long rest of you don’t have a special feature that lets you regain some quicker, so ultimately it might be best to split these into two feats and have more of the benefit be at-will in each feat, include weapon proficiencies.
Perhaps the feat should let you learn two light fighting manuvers, and give the defensive duelist bit and a minor boon for having a free hand.