Vettel, already the sport's youngest quadruple world champion at 26 years old, was utterly dominant in Abu Dhabi on Sunday as he chalked up his seventh successive victory with almost embarrassing ease.
No driver in the modern era has won more than seven in a row, and Schumacher and Vettel are the only ones ever to have done so in a single season.
Italian Alberto Ascari racked up nine consecutive victories but that was over the course of the 1952 and 1953 seasons - when the calendar admittedly had a fraction of the number of races seen today.
"The times are very different," Horner said when asked to compare Vettel's achievement with Schumacher's success at Ferrari.
"We're all on a standard tyre now, there's no testing, we're limited on the amount of engines we can have, the amount of wind tunnel time and so on.
"So it's a much more even playing field (now). It's always difficult to compare generations with generations but the level at which he's performing, I don't have words to describe how phenomenal it is. It's just truly impressive," added Horner.
Vettel finished more than 30 seconds ahead of second placed team mate Mark Webber in Abu Dhabi, the best benchmark of performance given that the Australian was in an identical car and had started on pole position.
He had been 40 seconds clear of the rest at his second pitstop.
Under the Singapore floodlights in September, the German's most dominant win of 2013 before Sunday, he had taken the chequered flag 32.6 seconds ahead of Ferrari's Fernando Alonso.
In India, he won 29.8 seconds clear of second placed Nico Rosberg's Mercedes.
"It was absolutely mind-blowing in many respects. After the start, Seb just got his head down and disappeared," said Horner of Sunday's latest display of supremacy.
In 2011, Vettel won 11 races - a number he has matched already this year with two rounds remaining - and is now on course to equal Schumacher's 2004 record of 13 victories in a season.
"It's just truly dominant, he has just hit a patch of form that is incredible. We know Mark Webber is a very fine racing driver and in a race that didn't have any safety cars or any issues, to achieve what he's done is quite mind blowing," said Horner.
"I think Sebastian's just stepped up another gear."
While others have struggled to get the most out of the tricky Pirelli tyres, or indeed make them last, Vettel seems to have unlocked their secrets more than anyone else - even if he denied there was any great mystery.
The tyres, he said, remained difficult to drive because of their extreme sensitivity but it helped to lead from the front and have clean air.
"Somehow we got the hang of it," he said. "More and more so towards the end of the year. And looking after them (the tyres), really listening to them and being able to extract maybe a little more performance than the other guys."
The comparisons with compatriot Schumacher have followed him throughout his career but the numbers tell only part of the story.
"The thing is that people see seven races. People don't see the challenge it takes every single race to nail it," said Vettel.
Webber, who has been on pole in two of the last three races but has yet to win a race this season, knows what it takes and recognised his team mate was simply 'on another category'.
"I think he's in a sweet spot, for sure," he said.
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