I'm also having problems keeping threat off my pally 'off tank'. I am very low on artifact power, as this character has only been 110 for like 3 weeks now so pally has me beat there.
Anyone mind looking at my logs and tell me what I might be doing wrong or should be doing better to increase my damage / threat?
https://www.warcraftlogs.com/reports/xAH3jm4yMPFDwnct