So, Ki cost, no weapon requirement, and and works on ranged attacks, in exchange for a smaller bonus that defensive duelist?Zen Defense
You have learned to harness and focus your Ki energy to the point that can you can defend against attacks with lightning speed. You gain the following benefits:
• You gain 2 Ki points. If you already have Ki points, your total Ki points increases by 2. Spent Ki points are regained after a short or long rest.
• When a creature hits you with an attack, you can use your reaction to spend 1 Ki point, allowing you to add a +3 bonus to your AC for that attack and potentially causing the attack to miss you.
Pretty meh for a non-monk.
Make the AC boost last until the end of your next turn? That'd make it a mini-shield at the cost of Ki.
Doesn't work for unarmed attacks as written; there is no weapon damage dice!Zen Offense
You have learned to harness and focus your Ki energy to empower your attacks. You gain the following benefits:
• You gain 2 Ki points. If you already have Ki points, your total Ki points increases by 2. Spent Ki points are regained after a short or long rest.
• After you successfully hit a target with a ranged or melee weapon attack, you can spend 1 Ki point to roll one of the weapon’s damage dice one additional time and add it to the total damage of your attack.
Remove "weapon's" and you get what you intend I suspect. I mean, a Rogue using a dagger could reroll a sneak attack die, but that isn't a problem.
In terms of ki-for-damage, this is ok. Normally it is MA die+stat but can miss. And this lets you burn ki-for-damage much faster.