Most swaged factory wadcutters are pure lead. Cast factory may be anything clear up to hard lead depending on the maker.
I can't say the softer lead makes them more accurate. I think it is more the production method(swaging) rather than the hardness.
I owned the NOE hollow based wadcutter mold. It shot fine. Maybe 1/2 inch tighter than my solid cast wadcutters at 20 yards. Since I am not a target shooter, that difference wasn't important to me so I sold it.
I have found that case sorting by headstamp makes more difference to my accuracy than the hollow base did.
My best loads are loaded into match wadcutter brass. I get very good accuracy with those cases. I don't think the brand makes as much difference as the fact that all the cases are the same.