IMO, you have a lot of the "not great" skills, such as New Iron Hammer and New Whirlwind Wave. While they are decent, their cooldowns are much too long. I messed around with them with a mule Sieg and couldn't bring myself to like them enough due to this.
My recommendations on your skill build:
- Max Cross Cut. Why not take advantage of the damage with True Rage if you are maxing it? It doesn't really make sense not to.
- 1 point in Blow and Counterattack. These are personal preference, but Blow is hard knockdown and it is good to use as an escape. Counterattack can save your life if you properly use it.
- At least lv2+ Iron Hammer. Lv2 stabilizes the damage, which is better; I would say max it because its damage potential is so amazing, hitting nearly 1000 x 6 or so at max. It's cooldown is one of the shortest of lv60 skills, as well.
- Take out New Iron Hammer and New Whirlwind Wave. Their cooldowns are too long, and by the time you have enough Dex in Myth, it still is too long compared to other skills.
- Crescent Moon Sword. While I like this skill, since it isn't physical, you could take it out to get more out of True Rage, but it is up to you. You could use Hurricane Sword instead, too, since it should be great in Myth; short cooldown, high damage (around 400 max?), and pierces mobs. However, I haven't really used it much and just couldn't get used to it.
- Whirling Sword. I would put at least 1 point in this skill. It's nice to have a ranged option that can hit multiple targets.
- Flash Fate. You could take this out or keep it; it's up to you. I didn't like it too much since it doesn't hit multiple targets like Whirling, but it does more damage and has more range.
- Kicking. Don't really need it, but it is up to you.
- Wind Kick. Up to you to utilize this with True Rage; it's pretty good at max.
- Flying Dragon Sword. I would recommend maxing this skill. It is a nice damage dealer.
- IMS. Lv4 isn't too shabby, but it does take awhile to execute. Again, cooldown staller/critical skill to use.
- Bless skills are up to you; I kept my Magic Defense at 3 to save points; will max later of course.
- HP Increase is not really needed; invest in it later if wanted.
That sums up my overview of Sieg skills in a stage/myth standpoint.