if you are using your MH Primary Skill to do most of your damage, then Skilled Mythic is better (I wondered about this also and did the math) than Brutal, giving better DPS over time. Brutal would give good Spike damage but a little lower DPS over time. if you’re not using your MH Primary Skill for most of your damage, then Brutal would be better.
Skilled & Exposed Mythics give the same damage of +50%. the only thing that gives Skilled the edge over Exposed is that Skilled gives +50% damage on the first hit, while Exposed doesn’t give the +50% damage until something is pierced, so the second hit at the earliest. on the other hand, Exposed works with any Skill, while Skilled only works with the MH Primary Skill. since Exposed does +50% damage, it would give better DPS over time compared to Brutal, while Brutal would give good spike damage at the cost of a little lower DPS over time.
Legend Mythology +50% gives +50% damage to Mythic Weapon Skills, like Cosmic Orb or Earthquake. Earthquake does 300% MH weapon damage every 0.25 seconds for 3(?) seconds while stunning enemies. with Mythology, it would do 450% MH weapon damage every 0.25 seconds for 3(?) seconds while stunning enemies. if your weapon does 1 million damage, Earthquake does 3m damage every 0.25 seconds. with Mythology, Earthquake would do 4.5m damage every 0.25 seconds.
when you get 10 or more Obsidian, put a Crystal +45% Attack Speed on either your MH, Chest, or Head, and replace Attack Speed on the other 2 with 1 Crystal +225 Crit Damage and 1 Epic Crit Damage so your high Crit Chance can be more useful for getting way better spike damage.
Obsidian can also be used to max the values of Crystal affixes. you have to have an empty space on the Item to do this (by taking off one affix or myth stone. after you max the Crystal affix, you can put the affix or myth stone back on the Item). when crafting, you would use Diamond to max any Legend affix values, Obsidian to then max the Crystal Affix, and use Fluorite to max values of Epic/Normal affixes. Diamond is first because it rerolls all Legend, Crystal, Epic, and Normal affix values at the same time, while Obsidian and Fluorite reroll only one affix value at a time.
nice build. it looks like it should be doing well on floor 1k or higher. just make sure you use Smokebomb for the auto Dodge for the next attack, since Sanctuary has a 30 second cool down. took another look at the build, and your Propulsion and Ambush Talents must be giving you some good Crowd Control.
Legend Multiple Attack and Ignore Resist can be rolled with Ruby, so maybe find a Bow with a Legend +200% Weapon damage? and you could replace that Epic +2 Extra Attack Chance with that Myth Stone that gives +4 Extra Attack Chance (if you have it or can afford the Gold to upgrade MS to get the one you need.
hope this helps, and welcome back to the DQ Forums @FlyingFish15 !