Regarding nu metal and metalcore

Those are all what I would consider real metalcore, all the bands considered metalcore these days sound nothing like these bands.

That's why the term "metallic hardcore" was coined. It emphasizes that the -core is actually HARDCORE as in the punk offshoot.
 
Why? It's a lot more useful these days given all the -core genres (metalcore, deathcore, crunkcore, etc). Helluva lot more descriptive than shit like "djent".
 
Djent, in its original meaning, is a heavily digitally processed power chord, and is the name for an elastic, syncopated guitar riff.[4] Djent as a style has been described as featuring heavily distorted, palm-muted guitar chords alongside virtuoso soloing,[2] and is characterized by its progressive, rhythmic, and technical complexity, often interwoven with polyrhythms.[7] Another common attribute of the style is computerized sound, as many of its acts, such as Periphery, Northlane, Fell Silent, Colossus, Concatenate, El Scar, Volumes, and Textures, started their careers recording at home and self-producing.

This sound became so popular that enough bands were using it to now be called a genre...
 
Why? It's a lot more useful these days given all the -core genres (metalcore, deathcore, crunkcore, etc). Helluva lot more descriptive than shit like "djent".

I'd say that it tries to shrug off the travesties committed by the popular bands in the genre. Metalcore is a simple enough genre to reference, there's no need to reach for purity. It's metal + hardcore, whether that's Terror-style hardcore or Black Flag-style.

It reminds me of Immortal calling themselves Holocaust Metal or Cobalt calling themselves War Metal.

We could, for example, talk until we're blue in the face about how 70's, 80's, and 90's space rock are like completely different genres, but nonetheless, as much as we attempt to genrefy the end results, the central idea of space rock has remained the same over the decades: long, unconventional songwriting, heavy use of effects, dopamine-driven grooves and introspective lyrics.
 
It's really like splitting hairs between brutal death metal and slam. Yea they're similar and draw from similar influences but in all honestly they're fairly different to the ear and people usually like one or the other.

Hell given your definition we could always lump brutal death metal, death/grind, deathcore and slam into metalcore, given their heavy influence.
 
No it's not. It's separating Killswitch Engage (metalcore) from Integrity (metallic hardcore). They're VASTLY different sounds. I'm not talking about different shades of hardcore versus metal, I mean the difference between Bullet for my Valentine and Pulling Teeth.