The slugs need to be as powerful as the KSG in BO2. I've only used them a few times, but getting hit markers from a pump action slug at short range is useless. The KSG rewarded accuracy and punished misses. The slugs in Ghosts feel only slightly more powerful than the buckshot(maybe two hits instead of three) with none of the spread advantage.
Semi auto's shouldn't have slugs, though.
I still want dragonsbreath shells for pump actions, with fire damage over time. They basically already exist as incendiary rounds in Extinction, just balance them for MP and make it happen.