Three Formula One world titles and 29 victories is some achievement for a 26-year-old, particularly given the highly-competitive nature of the sport these days.
Whether Vettel will ever threaten the seven world titles and 91 wins of fellow German and his hero in Michael Schumacher, naturally only time will tell, although Horner claims it to be "impossible".
Championship number four beckons this season, although a rare failure to finish after suffering a transmission problem in Sunday's British Grand Prix, has offered up a glimmer of hope to his rivals.
It proved Red Bull do have small chinks in their armour, although as far as Horner is concerned with regard to Vettel, he is the complete package.
Asked as to the difference now compared to 2010 when Vettel won his first title, speaking to Press Association Sport, Horner said: "It's his experience, his knowledge.
"He's always had tremendous natural speed, and he has an intelligence that goes with that.
"But as he's gained more experience, experienced situations of pressure, expectation, difficulty, he's learned from each and every one of them, and applied those lessons extremely well.
"That's just made him more and more rounded."
Critics would suggest with experience Vettel has become more and more ruthless too, as was the case in Malaysia this year when he grabbed a win after ignoring team orders to hold station behind team-mate Mark Webber.
"It's always beenthere," added Horner, speaking ahead of the German Grand Prix at the Nurburgring this weekend, a race Vettel has never won.
"It's perhaps become a bit more obvious to the outside world because of what happened in Malaysia, but there are other factors surrounding that.
"He's a fiercely-determined young man. You don't achieve the kind of success he's had without that burning desire and determination.
"But then he is also the easiest driver I've ever worked with. He doesn't have an ego - or certainly a very modest one.
"He enjoys what he does, he's extremely honest, he gives 110 per cent and he's a nice guy. It's not often you get that combination."
Horner further describes Vettel as "straightforward", and "his own man" given he is able to walk the fine line between being a star on one side, yet able to shun the spotlight on the other.
"He's dealt with the expectation extremely well. None of it has gone to his head," assessed Horner.
"He's fiercely protective of his private life and his friends and his family. He's managed to maintain a balance and keep his feet on the ground.
"But he still appreciates being a grand prix driver is something very special and very privileged.
"He still gets excited about the fact he's a grand prix driver and is driving some of the best cars in the world, which is really refreshing to see."
But as for one day emulating the most decorated F1 driver of all time in Schumacher, a dismissive Horner said: "It's impossible.
"Schumacher's domination, in a period where the regulations were as they were, is extremely unlikely ever to be replicated.
"Seven world championships and 91 victories? Unbelievable!
"Three at 26 is a hell of a score rate. To achieve another one would be incredible for Sebastian.
"But you can't look down the road at what he's going to achieve in his career. Who knows what could happen?
"You can't rule it out, but you can't expect it either and therefore it's better not to think about it."