Helping with dps and gear

[RmiiN 0]

so as i have seen so far i am doing less dps than any class in my guild dont rly know why but its always like im doing the least damage on atleast most of the fights 

i got pretty decent gear but still not getting very good ranks at mythic my hc ranks are not bad but when it comes to mythic im always below 50% need some help 

https://www.warcraftlogs.com/rankings/character/2066410/latest#boss=1777

http://eu.battle.net/wow/en/character/kazzak/Even/advanced

 

trinkets that i have are :  Rumbling Pebble (Mythic)   Vial of Convulsive Shadows (Heroic)  

Empty Drinking Horn (Heroic)

Unending Hunger normal 

Forgemaster's Insignia (Mythic) 

Discordant Chorus (Heroic)

Reaper's Harvest (Heroic warforged)

 

so what am i doing wrong due to logs ? and if someone can tell me what is the best lvl 100 talent for each fight