Should Dark Arts Come Back in 6.0? If so, What Should the Skill Do?

[Shurrikhan]

that reads to me to just be balance issues, not a fundamental design issue.

It is, but at the same time it's a balance issue that is very hard to avoid (has an increasingly thin balance point, often too thin to deal with varying situations) if the bonus given is merely "more of the same" (more SE potency, more PS potency, more DD effect, more DM effect).

While SE and PS at least had embedded secondary effects, and C&S, AD, and DP each had unique DA effects, the HW experience should have already made that clear. I think this is largely what Xeno is getting at. It's a balance issue, yes, but a balance issue that's so often made an issue because of a more fundamental matter.

my thoughts on Dark Arts is that its effects should be neither the former nor the latter, and just be a bonus that makes a action either more interesting or have a additional effect. Dark Knight's defensive strength or offensive potential should not rely on Dark Arts or need Dark Arts, or else Dark Arts will just split all actions in half between the do and do not need Dark Arts groups.

On this I think we here almost all agree so far.