Vettel is potentially a week away from winning his fourth successive Formula One world title after another cruise in Korea.
Despite two safety car periods, Vettel managed to keep his rivals at bay again to claim his third straight win at the Korea International Circuit, fourth in a row this season and 34th of his F1 career.
Closest title rival Fernando Alonso could do no better than sixth in his Ferrari, meaning there is now a 77-point gap between the 32-year-old Spaniard and 26-year-old German.
Should Vettel take the chequered flag in next Sunday's Japanese Grand Prix and Alonso is ninth or worse, the former will again be cracking open the title-winning champagne.
That will put Vettel in the same bracket as Fangio and Schumacher, the only other drivers to claim four consecutive championships, with the latter the record holder with five in a row.
Asked whether Vettel was one of the best drivers of all time, Horner said: "He has to be right up there - he has to be.
"The level he is performing at is unbelievable in many respects.
"We know Mark (team-mate Webber) is a very talented and quick racing driver and matching him against that, he has been hugely impressive.
"What has been really impressive is he has continued to grow and improve as he has gained more experience, and to have won the ratio of races he has is remarkable."
Suggested to Horner that down the years people will look back and put Vettel in the same bracket as Fangio and Schumacher, Horner replied: "Should he achieve winning four titles in a row they will have to."
Neither Horner nor Vettel are celebrating yet, however, even though it is now only a formality the fourth title will be won.
After leading for all but one lap of the race for a win that leaves him on the brink of greatness, Vettel said: "I'm trying not to think about it (the title), to be honest.
"I'm trying to focus more on the present. We obviously won the title two years ago in Japan, but there are still a lot of points to get.
"Even though it looks very good for us, there is still a chance for Fernando, so we have to stay on top of our game.
"Right now we're just having a good time, I'm just loving what I do, and we enjoy the fact the team is working very well."
Typically, Vettel controlled the race from start to finish, even with the appearance of the two safety cars - although the second was somewhat dubious.
The first followed a tyre blow-out involving McLaren's Sergio Perez which scattered debris all over the circuit.
The second came after Webber's car caught fire after the oil radiator was speared by Adrian Sutil's spinning Force India, sending plumes of black smoke into the air.
Initially a fire tender, rather than the official safety car, appeared on track to slow down the field, but the FIA confirmed afterwards it was authorised by race director Charlie Whiting.
Come the flag, Vettel beat Lotus' Kimi Raikkonen and Romain Grosjean into second and third, with Sauber's Nico Hulkenberg fourth ahead of Lewis Hamilton in his Mercedes and Alonso, with Jenson Button eighth for McLaren.
Naturally, Alonso is refusing to throw in the towel, although knows the writing is on the wall.
"Vettel is a very long way off in terms of points, and we cannot expect miracles between now and the end of the championship," said Alonso.
"Second place in the constructors' championship is probably a more realistic target, but one thing is certain, we are not giving up now and we will give it our best shot right to the very end."
As for Hamilton, 111 points adrift and now fourth in the standings after falling behind Raikkonen, he admitted to enduring "not a great day".
"After the second safety car, we lost out in traction to the Sauber (Hulkenberg).
"It was a nice battle with Fernando at the end, but it's hard to take when it's only for P5 or P6.
"It was just not a good race for us, but we have the chance to bounce back in Suzuka."
Paul Di Resta again failed to score a point for the sixth successive race after a spin midway through the race sent him into a barrier, whilst Marussia's Max Chilton was 17th and last.