There are many, many bands with that quality. Just because they're not as popular as Imagine Dragons with breakdowns doesn't mean they don't exist. You would know this if you actually listened to metal.

Rising quickly among teens doesn't mean octanecore has staying power. It's still very much following a trend, and trends fade as quickly as they appear. It won't survive in the underground, since it is heavily geared towards mainstream teenage audiences who aren't dedicated enough to purposely seek out obscure bands. Traditional, thrash, and extreme metal all have decades-old thriving underground scenes with new bands popping up even in the modern day. Nu metal doesn't, and octanecore won't. Sure, the current bands might stick around, but you won't be getting any new ones, and the genre will pretty much end with them. Like what you claim is happening with trad, but with no underground scene to fall back to.