I don't need to say what's been said a million times; Dark knight has too few skills and too many repeats, yada yada yada. Unlike what others say about it, Abyssal drain is at the very least a tool that can be used effectively in more situations than Sole Survivor. Sole Survivor is best used when there is no healer or you've MESSED UP and even then there's no guarantee you'll survive anyway. If you can kill the target, 20% hp healed isn't much compared to clemency spam or alot of warrior's kit. 20% mp restored isn't that much considering how much Dark Knight can generate already.

So, how can we effectively change Sole Survivor to be a proper tool for survivability while keeping it unique? Why not instead change it to a buff to the Dark Knight?

EX: For 15s every time an enemy on your enmity list is KO'd, be healed for 5% of your HP and MP

This helps keep hp up with big pulls, as well as keeping mp higher than normal near the end of a big pull. Of course this doesn't work well with smaller groups and still doesn't matter in raids.This could be fixed with a simple little bit at the end tacked on.

EX: For 15s every time an enemy on your enmity list is KO'd, be healed for 5% of your HP and MP. If the duration expires without a single enemy being KO'd, damage all nearby enemies by 10% of your current hp.

OR

EX: For 15s every time an enemy on your enmity list is KO'd, be healed for 5% of your HP and MP. If the duration expires without a single enemy being KO'd, for the next 5s 25% of damage dealt restores hp and mp.

I've only just gotten Dark Knight to 60, so I'm not sure if these seem super tantalizing by the people who main the class. However, Sole Survivor is currently very unappealing unless you're in a very specific situation so it's in dire need of a change.