The larger time period is 80s - 10s, so yes, these things are gradual. And you're right that the trend that dominates the 10s in particular started around '08, maybe earlier! But this doesn't mean you can just obviate the distinctions between decades. It's in FULL BLOOM in the 10s. That's the point. You're like one of these nerds who tries to really pin down when rock n' roll started. It's gradual, starting long before in many proto forms, really crystalizing in the late 40s, blooming in full in the 50s, developing that same classic form into the mid-60s, having a revolution, seeing that revolution develop into a new classic form, having that new classic form get demolished by punk, etc. These are complicated things! But don't let the complications bar you from seeing the big picture: things are more fucked than ever.