Relic weapons are balanced around a WS fairly unique to each of them rather than being particular to a job, evidenced by RDM being on Excalibur or PLD being on Ragnarok.
Let's say RNK isn't supposed to deal so much melee damage with their regular swings and WS lest they turn into a DRK with resistance or even invincibility to magic, so while they get most of the pre-99 'good' WSes like Spinning Slash they don't get put on Resolution. If you then put RNK on Ragnarok, a 99 Rag with the 40% damage bonus on Scourge would actually be a huge upgrade in WS power for them, roughly like going from Spinning Slash to Torcleaver, such that any RNK not toting a Ragnarok would be considered half-assed. Most Relic WSes never competed with or were at best a sidegrade to the top level 75 WSes, but after the renaissance most of those Relic WSes were obsolete and so were given the +25% and +40% damage bonuses to make them compete with the new, but more exclusive, Merit WSes. If you wanted to limit a Great Sword wielder's potential to the degree that you might not want to give them Resolution, you sure as hell don't wanna let them wield Ragnarok to get even lolScourge with that 40% damage boost.
For that matter actually, if SE wanted RNK to deal at least respectable melee damage, they'd leave them off Resolution but let them wield Ragnarok and put them on decent crit gear, or give them tons of tanky VIT gear and sneak them onto some particular 'WAR but not DRK' pieces and let them be pretty good with Calad/Torc.
So yes, it's a balance thing. If you don't get Vorpal Blade or CDC, Knights of Round is a staggeringly powerful WS in relation to your normal ones. If you don't get Resolution, Scourge easily beats out Spinning Slash. If you don't get Exenterator or Evisceration (less likely, I know), Mandalic Stab is a huge increase to your damage. If SE added Onion Knight tomorrow and they were given A+ GK skill and were put on Amano but didn't have access to Y/G/K or Shoha, Kaiten would be their top WS by a ridiculous margin.
SE might not want to create more raw-power DDs. Relic weapons and their respective WSes would be a 'back-door' to adequately powerful weaponskills that would undermine this. If RNK gets put on Caladbolg but doesn't get Resolution though, there's no reason they couldn't be put on Ragnarok too... well besides the goddamn +40 accuracy and 14% crit rate.
Giving them their own Mythic, though, gives plenty of 'working room' to balance a unique and adequate WS for them that plays to whatever gearing strengths they have. I wouldn't expect some crazy "damage increases with active runes" thing which may instead be on the mythic weapon itself, but instead it will just be a decent multihit WS with, I dunno, a good DEX/INT mod setup. I could only hope, though, that they would revisit other Mythic WSes at the same time, I'm looking at you 20% mods on Insurgency, and address the redonkulous cost of a Mythic weapon these days so these new jobs have more than a pigeon-fart-in-a-typhoon's chance at seeing that potential come to light.
Edited, Jul 26th 2012 6:35pm by Raelix
____________________________I've seen things you people wouldn't believe. Airships on fire off the shoulder of Bahamut. I watched Scapula Beams glitter in the dark near the Three Mage Gate...
There's always...not trolling him?
You're new here, aren't you?