The thing about Elena though is that her bloodline or whatever you want to call it started centuries prior with Katherine etc, as a petrova doppelganger. Yes the focus is on Elena but the story was in motion well before she came into it - the brothers, both completely in love with Katherine, turned by her into vampires. That kicks off Stefan's story as the protaganist because choices he made would come back to haunt all of them. Centuries later and Stefan finds himself back home, discovering Elena exists, saving her life the night her parents died. I think Elena was the focus or catalyst seasons 1-6 but watching the show in its entirety I always understood it, at the core, to be about the brothers, whether it's them fighting over Elena, saving Elena, fighting with each other, saving each other, navigating through centuries together etc.
I actually thought seasons 7-8 were a bit of a return to form for the show after a slow seasons 5-6. Parts of 5-6 I loved - Bonnie and Damon on the other side, Kai (one of their better Big Bads - I think I dozed through most of the Travellers storyline). Elena, Stefan and Damon were the heart of the show no question, but it did revive somewhat when Nina departed, probably because they were forced to focus on other things...and putting the focus back on the brothers instead of the triangle - which really had resolved itself by around season 3-4 - was a good move because Ian and Paul have their own great chemistry that had the chance to shine a bit more. Having said that I thought the Siren sisters was dragged out far too long - we got two seasons of them when really one would have been more than sufficient. Comes back to the plotting too - knowing it was their final season it was obvious that the final Big Bad was going to be their version of Hell; the ultimate in good versus evil and the idea of redemption and finding peace. Pronouncing Katherine as the Queen of Hell was a great idea and came back full circle to season 1...but I thought the execution was rushed and sloppy. To really drive home the Queen of Hell idea they needed to have Nina for way more than one episode, which wasn't possible. In that case I think they needed to pick someone else as the devil altogether, and maybe then they would have been able to put more focus on Nina playing Elena's return and her reunions with her friends. Really that's what everyone was waiting for.