If Crowfall's combat is to be skill based, it should not have RNG. Skill based combat means analyzing a situation and choosing the best course of action to turn that situation in your favor. To foster skill based combat, Crowfall should allow its players to learn from their past successes and failures and to apply that knowledge to future situations. This only works if players can clearly see what allowed them to succeed or fail in past situations, and if they can, to some degree, predict the consequences of their actions in future situations. RNG only obfuscates this learning process. For example, someone could blame a lost duel on a lucky crit his opponent had, rather than a mistake that he himself made.
One argument in favor of RNG in combat is that it adds variance to what would otherwise be repetitive fights. But Crowfall is a PVP MMO, where we will primarily be fighting players with their own customized characters and playstyles, instead of groups of identical monsters. There will already be a lot of variance from any particular fight to another even without RNG, such as gear and status interactions, along with the fact that no player can predict his opponents' actions completely accurately. Another layer of RNG explicitly coded into the game would make these carefully crafted, deterministic factors pointless.
One final argument in favor of RNG is that it gives less skilled players a chance to beat more skilled players, thus keeping the less skilled players interested in the game long enough to become good themselves. But a victory gained through RNG is less satisfying than a victory gained with the knowledge you spent effort to acquire. Besides, a less skilled player can still beat a more skilled player without RNG: we have all had times where, even as newbies, something clicks for a moment and we pull off something amazing. When we understand that something good happens purely due to our skill, unadulterated by RNG, we remember that experience and try to replicate it, becoming better players in the process. And even in defeat, no RNG is still better than RNG. When we lose because of RNG, the game feels unfair. But when we lose in a purely deterministic way, while we still feel frustrated, we understand the game is still fair and we retain our motivation to become more skilled at it. This is why I believe Crowfall's combat should not have any RNG.