To this day I've never seen a response that actually properly explained what TAI - NIN *ion stat does, but the best hypothesis I've seen is this;

Attack / Ninjutsu increase your damage by increasing your damage. Tai / Nin *ion increase your damage by lowering the enemy's Defense / Resistance.

Apparently Damage Reduction actually just lowers all damage you take by a percentage %, as opposed to lowering chaos damage as initially suspected, but the % is so small you need a LOT of it to matter. If following that line of thought it could make sense the Tai / Nin *ion lowers Defense / Resistance, the amount just is so small you need tons of it to matter.

Injury...not a * clue. Increases your crit damage (not chance) and lowers enemy's crit damage (not chance) on you, even mods say that. However nobody seems able to agree whether it works or not, not even mods. Some say it does, just needs tons and tons to do even like 100 more/less damage, others say its supposedly completely broken even at CN still.

Where'd you hear that from? Cause that's the first I've ever heard of it bypassing the dodge/block/avoid stuff Hinata and co' got.

Well color me surprised. All we need now is a confirmation on if injury actually works or not XD