Love the new idea about 15 point ability instead of m4 on the mastery tree.
So here is my suggestion.
Work in progress
Rend asunder : tactic no longer increase rend duration. Now increse rend damage by 25 % (both initial hit and dot part) . in addition rend instantly apply his 3 stack.
This change is to promote a dot playstil who suits well the savagery tree. It provide a good ability at the cost of a tactic slot.