I my personal opinion, based on current form this is how I list the best drivers after the top 3:
4 – Rosberg
5 – Raikkonen
6 – Webber
7 – Grosjean
8 – Schumacher
I’d argue Button, when happy with the car, is better than a Webber or Rosberg – but when he’s out of sync with the car, like now, then… “not really” is an understatement.
Not being happy with the car is no excuse for underperforming as badly as he is now. Hell, three weeks ago Hamilton won the race with the same car Button finished 16, a lap down.
One thing that distinguishes the top three from all other, is that they can optimize the maximum out of any car they’re given. Button can’t do that, he only performs when he has a perfect car underneath him. Webber is good, but not quite as good as the top 3. Raikkonen when motivated (but too bad he often isn’t) is on the same level as Vettel imo. Rosberg is getting near the top 3, and so is Grosjean.