I agree that 2-hander is the most damaging, but having the bonus action attack lets you spread the damage out to different opponents and when you can move between attacks that is pretty helpful. The shield master feat increases your and some of your allies damage output by letting you shove an enemy prone and getting advantage on attacks against it, it also helps against spells and effects. We also don't know how they are going to handle magic shields yet, if they give a bonus to AC just like armor at higher levels having a shield will be the only option to have ridiculously high AC.
I am not a math guy so not sure how all of this breaks down but, I think a well balanced group should have a mix of types a shield users to be on the front lines, a 2-hander for single target damage, and a dual wielder to take care of minions and stragglers.