People have questioned Vettel's status among the all time greats for several years now. The main reason was because there was no legitimate benchmark to judge him by. Mark Webber will forever be known as a fairly pedestrian pilot.
Now that Seb is taking a drubbing that is unprecedented in the history of the sport for a reigning champion, anybody who ever had any reservations about bestowing all-time status upon him feels justified.
Of course he can change that himself before the year is through however. If he's able to pick up the pieces as Ricciardo has now on 3 occasions, that will go a long way in silencing the critics. Until then, there's nothing that can really be said, he's been outdriven time and time again this season.