There is a bug with "Critical DMG Increase Mastery". It looks that adding points here totally reworks the buff only adding exc damage rate and removing the formula that adds crit dmg for every cmd points. As you can see in the screenshots the dmg decreases significantly: Before adding points:
Crit Dmg: 38,030 Exc Dmg: 41,809
After adding points:
Crit Dmg: 9,845 Exc Dmg: 13,624
Please check this bug.