Blade and Soul's combat system is a game less of dice rolls and more of evasion, blocking, countering and avoidance. It rewards you for stringing combos together and punishing missed attacks much like a fighting game. That said, there's always going to be a series of attacks that will hit you regardless. That's where the game's Attributes come into play. But what do these Attributes mean? What's important and what's not? Since this game has been out for a while now, there's been time for people much smarter than me to parse the numbers. So let's take a look at stats in Blade and Soul.
The bread and butter of all you do in Blade and Soul, Offensive Stats dictate the amount of damage you deal, the type of damage and the amount of crit - pretty standard stuff overall. If you know what Accuracy, Critical Hit, Critical Chance and Threat are, then Blade and Soul holds no surprises. There are a couple of somewhat unique stats at play, however.
First is Pierce, which circumvents an opponent's Damage Reduction and makes your hits cut through just a bit harder. Next is Concentration, which reduces an enemy's block bonus. After that is Mastery, which increases the length of time buffs stay on your character. Finally, we have the baffling Additional Damage stat, which...gives you additional damage. Somehow. It's not really clear how, to be honest.
On the defensive side of things, there are a variety of stats that are par for the RPG course; HP, Defense, Block, Evasion, Health Regen and Critical Defense. Overall, the defense stats are pretty much cut and dry, with benefits against a variety of damages that can be slightly surmounted by several attack stats. Primarily, high defense stats are best put to use in PvP, where you'd be facing much smarter opponents than what the PvE AI could ever throw you.
About the only stats that require a little extra blurb might be Willpower, which reduces the duration of debuffs and the Evolved Defense stat, which improves your defense against "Evolved targets" that can be found at the Soulstone Plains. Mercifully, this particular defense stat can be buffed with some drums found in camps in the area for 101 Prestige. It's an odd stat requirement, to be sure, especially since this particular target doesn't appear to be located anywhere else as far as I've found.
The Gem Factor
All of the stats listed above can be improved with Soul Shields, weapons, and accessories, of course. Another wrinkle in the cloth are Gems, which can be slotted into your weapon. The bonuses afforded by gems varies by type and can differ greatly.
Ruby gems can apply either a stun or additional damage on hit. Amethysts can either drain life or grant Recovery on a critical hit. Peridots apply a HoT on a successful evasion. Emeralds apply additional damage while blocking. Citrines applies additional damage to stunned or knocked down enemies. Sapphires can either do additional damage, restore HP or apply a damaging Slow effect. Lastly, Diamonds offer direct stat bonuses. On top of type, the number of sides a gem's shape has improves the bonuses provided. The smallest shapes are Triangular gems, moving up to Square, Pentagonal and Hexagonal shapes. Finally, there are different rarities of gems - Normal, Hongmoon, and Brilliant.
About the only thing that chafes about this otherwise nice system is the randomness. Gems themselves can provide bonuses that are randomly generated when they drop, and the gems in question only drop via loot boxes such as treasure chests or reward chests or from World Bosses. The entire system of customization is locked behind a wall of chance unless you're willing to pay for gems through the auction house. It's a good form of customization buried under a titanic mountain of RNG. Which might as well be manure, in my opinion.
Adding It All Up
With all of the factors at play, the prevailing wisdom for stats in Blade and Soul remains to focus on offense in the PvE space. If you're managing your rotations and avoiding the bad stuff monsters are throwing out at you in dungeons, then your defense stats will barely become a factor. By that regard, any passive boosts to defense offered by upgrading your accessories, weapons and Soul Shields are sufficient, though often a repeated suggestion is to have at minimum a 20% Pierce rating since avoidance by the player will save you much more often than letting the stats handle things. As for PvP players, the widely accepted logic is to still put a focus on Offensive Stats, with a little extra care given to Crit Defense, Defense, and Willpower.
Across the board, Crit Offensive Stats are the ones to focus on in terms of Soul Shield bonuses, equipment, and gems. Attack Power is important and tends to be the prime metric that most PUG endgame dungeons measure, but stacking on heavy AP can generally be not too valuable without a very healthy dose of Crit. It's also frequently recommended to have a minimum of 90% accuracy, as most endgame bosses tend to feature high Evasion. The name of the game is to hit hard and frequently.
Depending on your class, the type of gem can have a great affect on your playstyle, and thus can further affect your stat build. Citrine, for example, could be useful as a Destroyer since most of my rotations apply stuns. Peridots or Emeralds could be useful for Assassins or Kung-Fu Masters. Rubies certainly can be beneficial to all. However, Diamonds are a girl's and a guy's best friend, especially if the Diamonds in question provide the best stat benefits.
Overall, the stat sheet in Blade and Soul is a mixture of interesting potential and missed potential. Some throwaway stats are kind of the nature of the beast in MMORPG stat sheets, but there are more than a couple here that could have made life a little more interesting and shake up how each class operates. On the other hand, with that fighting game analogy in mind, Blade and Soul really is a bit more proactive than reactive. It's easy to ignore the stats since weapon and accessory upgrade paths do most of the work, but it still is a good idea to take a look at your stat sheet once in a while!