If the quip raised only a hollow laugh after the most dominant season ever, with triple world champion Max Verstappen (26) setting a string of records including 10 wins in a row and 19 in total, it was because it contained an underlying truth.
Red Bull will hope to defend their titles in 2024, when there will be a record 24 races, with an even better car.
"This car is going to go down in the history books as a very, very special car," Horner said of the RB19. "To have won 21 races out of the 22, just missing out on Singapore, it leaves room for improvement.
"You're always looking to find marginal gains," he continued.
"It's never enough. We know our opponents, this will have motivated them more than ever to come back at us hard and nothing stands still in this sport. Everything moves so quickly.
"You could see as we weren't developing, the opposition coming closer and closer. We're going to hopefully take all of these lessons out of this car and apply it into our 20th car, RB20, next year and try and defend these two titles."
The big question on everyone's lips is how much their rivals can raise their game, as they surely will.
The final gulf between Red Bull and closest rival Mercedes was staggering - more points than the once-dominant second-placed team, who failed to win a race for the first time since 2011, managed in total.
Verstappen alone, with a record 575 points, scored more than Mercedes' 409.
Sergio Perez (33) was eclipsed by his teammate, with plenty of speculation about his Red Bull future earlier in the year, yet still finished overall runner-up.
"He'll take a bit of time this winter to reflect on where he needs to improve and I'm sure he'll come back fighting next year," said Horner of the Mexican.
So dominant was Verstappen on Sunday, winning from pole with fastest lap, that he even delayed his final pitstop to ensure he became the first F1 driver to lead 1,000 racing laps in a season.
"There is a Mount Everest to climb in order to catch up with Red Bull," Mercedes team boss Toto Wolff (51) told reporters on Sunday.
His seven-time world champion Lewis Hamilton (38) agreed: "Red Bull won by 17 seconds and they have not touched the car since August or July, so you can pretty much guess where they are going to be next year."
The next major rule change is not until 2026 but Formula One boss Stefano Domenicali pointed to McLaren, the most improved team after an uncompetitive start, as an example of the jump that could be made.
He also looked at the qualifying timesheets for further support.
Despite their dominance, Red Bull took 'only' 14 poles from 22 races. The difference was that Ferrari's Charles Leclerc (26) failed to win from any of his five while Verstappen triumphed 12 times out of 12.
"You saw yesterday in (first) qualifying, 20 cars in (separated by) less than one second. So in qualifying we are very, very close. Of course race pace is different," Domenicali told Sky Sports television.
"I think this will be the major thing we are going to see different next year."
