Everyone has at least a Relic or Empy if they have played for any significant amount of time and actually wanted to take the time to make one. Very few, and fewer still since people quit, have Mythics. They are clearly the most time consuming and are the only one of the prestige weapons to require multiple people working together to build, regardless of level (if you aren't paying for multiple accounts or cheating). Furthermore, Mythics make up less than 5% of the total amount of prestige weapons in the game in last year's census. Don't sugar coat Mythics. They are hard to get and more take time compared to almost anything else in the game.

These should be custom tailored weapons that should be balanced around the individual jobs that can use them. They should be the best weapons in the game for every job, especially since they take the most time invested to acquire. There is no reason you shouldn't make each Mythic outlandishly good for each job, since only 1 job can use it. Not necessarily in the form of total damage (even though AM3 generally accomplishes that), but SOMETHING that every job should go, 'well damn, I really want that' See Yagrush for valid example. Some Mythics are kinda close, but others really could use a lot of work considering how much the game has changed.

That being said, their SC properties are fine. Pretty much all Mythics have lvl 2 SC properties that make dark or light if you combine them with the appropriate other lvl 2 SC property. (Not so much on Yagrush, oh noes not the Melee-WHM, SC makes them broken powerful...said no one ever.) At the end of the day Lvl 3 means you have a 50% chance of making a SC on accident and Lvl 2 SC properties drop it to 25% (unless it is double lvl 2 like RDM and BRD mythic WSs). SCs don't really work against a lot of mobs anymore because of higher tier mobs ridiculous magic evasion, -MDT, MDB, or something else that makes SC damage increasingly unreliable. Against most things that you would fight with a small party you can still probably SC things dead, much like I do, and enjoy it. The issue really isn't the Mythic WSs SC properties, and is actually SCs in general becoming more and more antiquated.

The other advantage to lvl 3 SC props is that you just spam the same WS back to back and get SCs. IMHO that is a mildly lazy approach to SCing. You can generally have access to Trial, Mythic, Merit, and a Prestige WS all at the same time. It's just not that hard for most jobs to make Dark and/or Light anymore.