Fighters have always just been melee ADCs, bruisers accounted for the ones that were required to build tanky self proclaimed by people, therefore becoming colloquial. Riot just finally put an official name to it. The word bruiser came from what a bruise is, being something hitting hard and hurting, but not at an incredible rate.
Things like Disruptor, enchanter, controller: Those are Riot trying to enforce a subclass system somewhere it does not need to be and will not be used. Like I said, people, not Riot, referred to tanky fighters as bruisers. In fact, bruiser was not a recognized term by Riot. That was all players. Riot called them fighters. Finally, they applied the name Juggernaut as the word "bruiser" wasn't quite professional. No one will say "We need a vanguard/warden". We need a tank.
POINT IS: This post highlights the problem of this subclass system. Yes, Olaf is a diver for a short window of time. However, if his ult is on CD, he is no longer a diver. Now he is a juggernaut. See the issue? Shyvana is a diver only once every while. She performs this "dive" function in a mathematically insignificant portion of time in the game. She is mostly a juggernaut for most of the game.
This is opposed to someone, like Riven who can constantly dive due to her mobile kit, or Yasuo and his ult.