I think part of the issue with armor items is that they have too much overlap

Riot apparently doesn't want people to pick their armor item based on which one is most cost effective, but rather what it offers in the passive/active department.

Okay, that's fair.

But the problem is that there's an awful lot of overlap between what the various Armor items do.

I want to be tanky and slow things: I want to be tanky and ruin the ADC's auto-attacks: I want to be tanky and deal more sustained damage (sorta ) I want to be tanky and get around the map faster (yay, something that's actually new)

If Riot really wants Armor items to be picked based on the neat passive/active they grant rather than their raw stat efficiency (defensive items are already among the least cost effective items in the game) then should said items be given a little bit more distinction from each other? Do we really need three slowing armor items? Do we really need two attack speed slows? Wouldn't it be better to give them each a totally unique (and strong) niche rather than having them all stepping on each others toes?