Hack should not be skipped, but Slash should. You could get by without Slice in Broadsword if you wanted to. Eventually if you can cap your melee defense without it, you could skip Parry, but for leveling it is excellent (but you might want it anyway for defense debuffs, or for the enemies on the new trials which have higher tohit).
Grant Cover is useful but skippable, One with the Shield can be skipped if you need to. Everything else in /Shield is pretty mandatory.
First time scrapper.. Hes currently 26 and the only thing I've skipped was confront and hack... And I took everything else for shield.
Just curious if there were any skippable powers that don't add to much towards DMG or survival.