we would need to see what the differences are between your Builds. your friend might have affixes that affect damage that you don’t have.
this is what affects your weapons damage before you consider skills, talents, and any other affixes or Mythics. the Critical Hits is figured out after all other damage modifiers are considered. also, some damage isn’t shown, because they are conditional. Defiant Set gives +25% DMG which shows on your Weapon, and +5 damage per Rank of your missing HP%, which doesn’t show on your Weapon until your HP goes below 100%.
hope this helps you figure out why your friend is doing more damage.