The whole point of the precision tree is to build on hit (botrk for example) and attack as much as possible. This deals % health damage so you don't actually need damage in the rune kit. If you want more damage you build more damage items, or take a different set of runes.
12% more damage from ALL SOURCES from Press The Attack is too strong as it is right now, and you can mark my words you'll see it nerfed in the next balance patch.
Edit: When you hover the precision tree it even says "Improved attacks, sustained damage"
if you want burst you should go to Domination tree where it says " Burst damage and Target access"