Sabot slugs need a rifled barrel to perform with any form of accuracy past 25 yards, which absolutely destroys shot patterns to the tune of 36" patterns @ 15 yards. So if you have a rifled shotgun barrel you have a slug shooter and that is it, in other words a rifle.
How do you figure that? I can swap barrels in my 870 a whole lot faster than I can my M1A. With a slug barrel and a bird barrel, I have much more than a rifle.
The OP said one gun to 'rely' on...that means one gun to do it all in the field and on the street not on a gun range.
Guess we all do have to agree to disagree.