Fracture is nowhere near a 6% dps increase, if you factor in off GCD abilities, dots, etc. I want to see parses on dummy with and without it that show anything near that. As said, someone reported 10-15 dps increase, which is 2.5% of a mnk's dps. 6 % increase would be 30 dps from 500. Are you seriously saying using fracture can improve your dps by 30 ? I kinda doubt that.

As for downtimes: on tether you don't have to stop hitting, only on wild charges. Once again, fracturing adds wil wreck your tp, i would much rather have my brd use his dots on all adds, will be much more effective.

On t11, we do manage to have our mnk do rear rotation during non tank tethers, and stay on boss full time for river, and for forked lightning its a 2 sec downtime. On t12, bluefire can be handled by a bard so that mnk get 100% uptime, fracturing adds once again destroy your tp for no big increase.

Look if you have a ninja goading you 100% of the time good for you. In my experience, giving some love to the brd provide much greater benefits than only focusing on the mnk, and fracture seems like a bad reason to keep goad for the mnk only.