monk? nerf the azura skill! End of story! 
Have you ever tested this in Colo, WoE or in quick-succession duels? You should have noticed that a cooldown of 60sec is a bit different to a 20sec for Rage Strike, 10sec for Shadow Explosion or 8sec for Cross Impact. Using my current Battle Tactic value for the Rage Strike, the result of a crit. hit is equal to any skill with a 7,000% damage multiplier... but hey, BT is balanced!
But you're right. Nerf G-Fist and there wouldn't be any monks left in the game.... end of the story.
Monks on RO2 doesn't really shine. If one can think about it the other classes has more use than a Monk. and they do it better. Monk as a Tank? A good Knight, BM or even a warrior and even in extreme cases even a Priest can be a better tank, heck a priest can generate more agrro than a monk just by healing alone.
Being a good tank isn't determined by your threat level alone. Knights and Warriors can produce an insane value (thanks to BT), but beside of that they aren't any better than a monk. In fact, the monk might even end up as a better tank due to SSS and Ki-Protection.
Beastmasters on contrast might have the lowest threat generation of all four tanks, but compensate that by insane HP values and insane heals, that makes them almost impossible to kill. So as long as a BM can keep the agro, he is a very formidable tank.
Problems only occur, if multiple tanks start a threat race to become the main tank...
How about a damager? Sure we get boost on power because we have FE and TSS. Well TSS only effects the one you shot with it. FE although gives you a good 30% power you need to have 3 spheres. Once disabled or even lag FE becomes useless in my opinion. Oh we do have an asura! Ok but when did we in reality has it been really reliable? Asura can't one hit kill anymore unless you're opponent is lower level than you and isn't even well equipped.
First of all, I guess you meant Throw Spirit Sphere not Summon Spirit Sphere here.
Fury Explosion (FE) requires 3 spheres, because that skill is better than other alternatives: Concentration or Berserk. As a compensation, Asura Strike a.k.a. G-Fist doesn't require any. If you don't like to be stunned while casting FE, you should talk to players of other classes, who might get interrupted while casting Awake, Tempest, Mark of Shadows, etc.
Asura IS reliable. Even if it doesn't one-shot certain enemies (try to equip 2 T2 parts with JeHoon runes), you can use Summon Spirit Sphere (SSS) to reset your cooldown and land a second G-Fist without to need to cast FE again. So monks still are quite powerful in 1vs1 situations. However, due to the extreme cooldown, a monk doesn't do much between these attacks.
IRON SKIN:
IMO, your comment about the efficiency towards "get hit by Crits or is being targeted by magic or a skill/attack with penetration" isn't true. AFAIK, the armor penetration reduces your total defense rate... i.e. happens before the cap applies. So a 15% armor penetration would reduce a 90% defense rate down to 75%, making the monk quite good against penetrating attacks.
Against DoTs (guess that means "Magic"), the monk is still slightly better than a Warrior or Knight, because Steel Body grants him a higher HP total and Ki-Protection has the higher value and allows the monk to stay mobile. In regard of crits, high dodge // parry rates might suffice... and the stat bonuses for the monk are already good:
Per relevant stat point:
Warrior: +1 hitpoint, +3 atk, +1 dodge, +2 parry, +1 crit
Beast.: +3 hitpoints, +2 atk, +2 dodge, +1 parry, +1 crit
Knight: +1 defense, +2 atk, +2 dodge, +1 parry, +1 crit
Monk: +2 defense, +2 atk, +2 dodge, +2 parry, +2 crit
Sure, the current defense bonus is crap (partly includes the def/vit part as well), because it's all too easy to achieve 75% defense rate of even 90%. The additional points from Iron Skin would result in only a few extra percentages.
The defense bonus was once quite useful, because it balanced out the differences between a DPS monk and other DPS classes. The monk wears cloth armor, so an Assassin got 50% more defense to start with. With AoV, devs did the best to ruin the game. So the assassin now starts with twice as much defense, whereas the heavy armor of Warrior / Knights starts with 4 times the value (also getting 4 times the refinement bonus).
Gladly, the monk got at least the additional defense bonus via VIT. Of course the devs could have altered the skills, not the stats, but hey... it's Gravity, not logic we're talking abut. So in order to make the skill viable again, the devs only have to either fix the defense formula or change +50% defense => +10% damage reduction (or add another passive bonus, like a +20% parry rate).
SPIRITUAL CADENCE
The skill was required, because as an Acolyte your gear only grants INT. Back then, the additional ATK from INT also compensated the lack of AGI. Since you're now getting a complete set of gear tokens AND a free stat reset, there isn't really a point in Spirital Cadence anymore.
The weapon power of the monk is quite ok, especially if you include the high skill multipliers. What ruins the show is Battle Tactics. Because a single critical hit can result in 6 times the damage, the average DPS also receives a significant push that makes Warriors so OP.
Right now, many classes seem to demand armor penetration for whatever reasons. I doubt that "a small fraction" would change a thing, but why not alter the formula first and then implement 1 WIS = 1 AP. Would love to see those WIS builds ^_^. But honestly, I still prefer a proper defense formula.
PROTECTION. KI
The short duration part makes it more powerful and therefore quite a good counter against boss AoEs and DoTs (DoTs are affected by damage reduction). Thanks to the cooldown reset and thanks to the fact that he stays mobile, the monk gets a good advantage over other tanking classes.
A 120sec cooldown or more for a 10sec effect (Ki-Protection, Endure, Shield Fortress, Feral Defense, Assumptio, Ice Wall,.. ) is still too much. In most cases, the average benefit is only 3~4%. That's even worse than some seed runes. So my suggestion would be to reduce the cooldown to at least 90sec, even better 60sec at maximum level, also making the cooldown the level-relevant part, not the damage reduction (see Shadow Armor).
LIGHTNING CRUSH
This skill could receive an improvement but it is far away from being awful. You can lower the cooldown to 2sec or less given enough vigor. Something that can't be done with most other skills like Brandish Storm, Grand Cross, Lord of Vermillion or Meteor Storm. If you achieve a 2sec cooldown, LS is as effective as a Brandish Storm without BT.
In my opinion, the worst part is the skill animation. Why would a monk jump in the air just to hit the ground? That would fit more to dwarves with axes or so. My idea of a monk is that he would perform a roundabout kick.
In general, I agree that some AoEs deserve a slow debuff, but I'm not sure if LC would be the right place. A simple fix would be to further increase the damage by xx% as long as Fury Explosion is active instead (see Grand Cross // Lord of Vermillion or Meteor Storm).
LIGHTNING WALK
The issue with being too close also affects other classes like the Knight (Shield Charge). On contrast, both skills are auto-aim attacks. And that's also the reason why I wouldn't like to be AoE skills (cause then, a Warrior's Battle Leap would have to be an auto-aim as well).
A push-back is hard to implement in RO2, as this would require to enforce a movement and could push your target over edges or more likely bug them. So enjoy the 5sec stun instead.
FURY EXPLOSION
Why do you want to make this skill a "aura of thornes"?
Why not fixing all the ATK boost skills instead by either making the skill effect more like a "power-rune", increasing the total damage or by adding the weapon damage to the ATK stat once again. It shouldn't be hard to transform the refinement bonus into an appropriate ATK bonus at least... the devs did something similar with the Bible already.
__________________
Although this sounds like I disagree with everything, I didn't want to offend you... This is just meant to be a feedback. In my opinion, the biggest issue of the monk is that he hasn't a well-defined role. Should he be just a tank without BT? Is he like an Assassin without hide & speed?