If you’re purely going by titles it’s Shinji Saito.
I think there’s a serious argument for Shinji, Takeshi, Hajime, and Mickey(Hiroyuki).
Shinji has the most titles with 13, which include all 4 combined division titles when they were held, showing mastery in all 5 styles for the time.
Takeshi has 7 titles, 2 time 1a runner up(ROBBED), and 1 time 3a finalist(and very likely could’ve been more if he was interested)
Hajime has 7 titles, and the only person to win in 2 main divisions in the same year, with complete dominance in both as well. His most recent worlds 4a freestyle was also one of the most innovative and groundbreaking freestyles of all time, to the point of having people completely question the judging system.
Mickey has the least titles and is the least versatile but has shown dominance in a way nobody has come remotely close to replicating in what is by far the toughest style. A lot of people know he has 4 1a titles, but many don’t know he is also a 5-time runner up and made finals in 16 consecutive years.
It’s hard to compare Mickey vs the other 3 but I think he will always be in the conversation for GOAT just because of his dominance in 1a. Aside from him tho, I think the other 3 are pretty even but I think Hajime will definitively edge out the other 2 by the time he retires. Still too dominant in 3a and 4a right now and if he picks up another style it’s GG.
Honorable mention to Rei Iwakura, 6 titles and 5 podiums in arguably the hardest x division style to consistently do well at.