I don't know where you come up with this stuff, but it's clearly not based on experience and clearly based on a general dislike of Fenders. Which is fine if you don't like them, but your prejudice against them is doing the talking vs real world experience. I can get any sound out of a Fender that I could ever need for any style of music, including these nu-metal styles, and I can also get the action as low as I can on any other bass. Now maybe it won't sound exactly like the sound Sven Armstad-Torgesson got on the second song on Baby Evisceration's 11th album using his Warwick Dingwall Mothman, but it will certainly sound good and proper for that type of music, and it will play as easily as you can make any bass play. And that includes their 5's. You may not like them, but just because you can't make them work for you doesn't mean others can't.
There is no magic on this planet that makes a passive Fender 5 jazz 34" scale bass sound like a 35" scale or longer with active dual humbuckers.
If Fenders, or the multitude of knock offs, could be used in fast aggressive music they would be. But they aren't. The closest I'm aware of is Brandon Michael of Allegaeon who plays a Fenderish looking 5 with a P and humbucker set up. There is also Gabe Crisp of Whitechaple who plays an ESP PJ that looks like a 4 string Fender, but he isn't quite in the same league as some others.
Fender 5 necks are massive, and very heavy. As I said, to the best of my knowledge there isn't a regular production 6 string Fender bass. They have never embraced newer electronics, and their finishes are firmly stuck in the past. I don't the they know the word Ergonomics.
Look, Fender isn't your girlfriend. A bass is a tool and you need to use the right tool for the job. My Spector basses are totally wrong for A LOT of genres. They aren't the right tool for that. If a Fender Jazz 5 was good for death metal, djent, metal core, tech death, groove metal, or death core, people would use them. But they aren't. And to tie this specifically to the OP, it is because they (we) use their B (or A, or G, or F#) in ways that someone playing a Fender, or Sadowsky, or Lakland generally wouldn't. And in these genres, where the full scale of the bass is used because of many techniques happening through out the song (sometimes in the same measure) they need 5 or 6 string basses. So as I see it, they aren't on their way out.
I pay very close attention to the players in the genres I'm playing. When I played doom\stoner metal I played passive PJ and J basses because that is what was required. When I switched to a more modern metal band I looked around at these absolutely insane bass players and realized that not a single one played passive 4 string classic\vintage style basses. So should I follow your advice, or take the lead of the guys playing, releasing, and touring on the music I'm listening to and playing?
PS- Is there a band called Infant Annihilator? Yes, they are hilarious. Is there a band called Dying Fetus? Yes, and they are awesome, as is their bass player Sean Beasley. There is also Decrepit Birth. I can name bands with F'ed up names all day long. Maybe you should check them out. Who knows, you might like them.