Wani's Rough Guide to an Un-HP-washing Dark Knight

You're not the first person to suggest rush before hex, but I'd also heard more than L1 rush isn't that useful, and I haven't heard much more about why a higher level rush is useful. Is pushing monsters a bit further that handy, or does it have other uses I'm not aware of?

As for achilles, I think you're underestimating how useful it is. I've heard a lot of dark knights say it's very helpful for staying in berserk because the damage you take while training is a lot less.

btw, how HP washed is "slightly"?

I think that having a higher leveled Rush will be a lot better, but not entirely necessary.
If I had to choose between Hex or Rush after Achilles, I'd with with Hex.
Personally, I would max it.
If you're going to use an apple, then don't summon it; chances are, you won't be using an apple during bossing events because they are namely given to ranged characters.

Point is, Rush has been effective at lvl.1 ever since Leafre came out.
It's not like other skill such as Hex, Aura or Berserk, where it's useless at lower levels.