Yes, this is what I have experienced against multiple conjurer types, too. You do have to "help" your summons against other summoners, or you just see an endless summons-against-summons battle. My mage uses her "Paralysis-Stick" to knock down the casters, and throws in an occasional "Wizard's Fury." (And yes, if it were up to me, and not up to my character, the "Wizard's Fury" would quickly take care of most of these battles. )
Yes. You got it exactly right. In Sevirus' case it was merely an academic exercise and of no consequence either way.
Another unmentioned aspect of conjuration is the ability to turn the undead. Very useful against Necromancers.
About bound armour, Sevirus had a spell that conjured a full set of Daedric armour. As best I recall, he eventually abandoned the spell in favour of the real thing.