Ok, enough is enough about the confusion of bruisers and fighters.
Look a lot of people have lumped all sort of classes and what not as bruisers and figther and don't know how to properly classify what is what so I am gonna make things crystal clear.
Fighters is a class that consists of Divers and Juggernauts.
Bruiser are melees that want to in and excel in close further combat and consists of fighters _and _ skirmishers as they also want to get in close to deal damage.
The difference between Fighters and skirmishers is that the later is frail and have doesn't have raw tankiness.
Assassins are NOT bruisers despite being melee because they can't risk getting into a brawl but skirmisher despite of them being frail can fight in the thick of a teamfight due to powerful defensive tools and sustained damage allows them to be better suited to get life steal.
Simple.