With an official rating of 140, Flightline equals Frankel's benchmark set in 2012 under the current system.
Previously, the highest rating given to a dirt horse was the 135 achieved by Cigar in 1996.
Flightline retired unbeaten in six starts, earning his historic rating in the Pacific Classic at Del Mar in September, which he won by a staggering 19 and a quarter lengths from Dubai World Cup hero Country Grammer.
He also won the Metropolitan Handicap and the Longines Breeders' Cup Classic in 2022, with the latter contest picking up the award for the world's best race.
Trainer John Sadler was understandably proud to see Flightline match Frankel's rating, saying: "He never hid his talent - he was a star from the day he walked into the barn and that's the way he walked out.
"We're so grateful to have a horse like this in my career. Most horsemen never get one like this, so I feel very blessed.
"We watched Frankel run. Racing gets more international and we follow what's happening over here so we thought that was kind of a good comparison.
"I'd like to thank Longines and the International Federation of Horseracing Authorities for this wonderful party. Everybody has treated us fabulously here in London.
"I think another point that works well is that this horse ran medication free, which I think fits really well into the international community moving forward."
Flightline has inevitably drawn comparisons with American legend Secretariat, but Sadler prefers to focus on his own horse's achievements and is already looking forward to what he can achieve in his second career as a stallion.
He added: "The comparisons to other horses are kind of joy killers. There's no win in that as they're all great horses and it's hard to compare horses from different eras.
"He's certainly the best we've seen in America for quite a while because of his brilliance, the fact that he can be so fast over a distance of ground.
"The story will keep going because he's so well-bred, out of Tapit who is the leading sire in America. It doesn't make it happen, but he's got all the check marks of having a brilliant next career.
"His racing career was what it was. Each horse writes its own history and we did what we felt was best for this horse, not necessarily what was best for us. If we'd had our way we'd have raced him for another two years or something.
"But for Flightline it was time for him to go to stud and he's got a really beautiful book (of mares) right off the bat, so he's going to have a great opportunity."
With the pressure now off, Sadler is delighted he is finally able to bask in the glory of what Flightline did on the track.
"We had a great party when we got back to Los Angeles and this has been a great trip for me. We've been here two or three days and it's been a lot of fun," he said.
"It warmed my heart when we were running in the Breeders' Cup Classic and I'm putting the rider up and John Gosden, who did his early years in California, was right there as a fan.
"Flightline never disappointed. When he's running it's hard to be aggressive and say he dominates because it's kind of bad luck. Now that it's over now we can enjoy it a lot more."
Drew Fleming, president and chief executive officer of Breeders' Cup, was elated to see the Classic named World's Best Race and admits Flightline's display will live long in the memory.
"It was truly spectacular," he said.
"I was very fortunate to watch Flightline run in the Met Mile and then go on to the Pacific Classic and there he just kept going and going - and the journey didn't stop.
"Flightline came to the Breeders' Cup and it was like The Beatles walking into the paddock - it was amazing. And then to see Flightline around the turn, in a beautiful Keeneland, it was just a truly magical day."