TLDR: IMO, Hajime is the GOAT, but Shinji Saito, Hiroyuki Suzuki, and Takeshi Matsuura have great cases as well and I think they are the only 4 that really have a solid case for GOAT.
The GOAT debate has always been a very interesting one for me that I’ve thought about a lot, and if we’re focusing primarily on comp (which I think is the most objective way you can go about this very subjective question), I think there’s only 4 people that can really be in the discussion IMO. Shinji Saito, Hiroyuki Suzuki, Takeshi Matsuura, and Hajime Miura. I think Rei Iwakura is a pretty clear 5th and everyone else is at least a notch below, but I very much consider those 5 the “Big 5”.
Shinji Saito - 13 world titles, most ever. DOMINATED all 4 years CB division was a thing and some even say part of the reason CB was discontinued was bc Shinji was TOO dominant. Most world titles, GOAT of 2a, most versatile player across all divisions in his prime.
Hiroyuki Suzuki - I see Gentry mentioned multiple times here but I think he is really not at the level of any of the Big 5 I mentioned. Mickey is still the undisputed 1a GOAT in my eyes and I think many people nowadays don’t know how dominant he was in the division compared to anyone else ever. 1a is by far the most competitive division, and Mickey is the clear GOAT of 1a imo, so I think he has to be in the all time GOAT discussion even if he has less titles than some x div players. GOAT in 1a, by far the most competitive division. 4 1a world titles. 5 additional 1a podiums (2nd 4 times). 15 world finals, the most of any player ever, and all in the most competitive division at that. He was a serious contender for 1a title NINE YEARS. NINE.
Takeshi Matsuura - 5a GOAT and also arguably the greatest 1a player to never win a 1a title. 7 5a world titles, 2 1a podiums (both 2nd), 4a 1a world finals, and he also placed 4th in 3a one year. I have no doubt he could’ve been pretty successful in 3a if he chose to compete in that div more as well. I think the fact that he was so successful in 1a helps his argument for GOAT a lot and it’s what keeps him in the discussion with Shinji since it’s the most competitive division, and he’s really the only x div world champion that’s been able to heavily contend for the 1a world title. 5a GOAT, arguably greatest 1a player to never win a 1a title, also world class at 3a.
Hajime Miura - 3a GOAT, 4a title. Only player to ever win worlds in 2 main divisions AND in the same year, and in dominant fashion too. Arguably the greatest losing performance of all time (4a 2019). I think Covid taking away potentially 3 world titles from him hurts him here but him still being able to win in dominant fashion in 2023 shows he is still the best. I also think his success in 4a really helps him the GOAT debate here. 3a GOAT, only player to win world title in 2 main divisions AND in the same year, and legendary '19 4a performance.
I think these are really the only 4 that have an argument for GOAT, and I think it’s close enough between the 4 of them that it simply depends on what you value. World titles? Skill in multiple/all divisions? Priority for 1a accomplishments over x div? Prioritizing dominance recency? etc. Personally I have Hajime as the GOAT but I think it’s really close between these 4 and I’ve went back and forth a lot, though I think I’ll have Hajime squarely as my GOAT with a few more world titles in his bag in the future (unless Mir wins the next like 4 worlds in dominating fashion or something 
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Honorable mention to Mir Kim who will have a great case for GOAT in the future if he keeps up this dominance, but I think it’s too soon for him to be in this discussion. I think Covid unfortunately nerfed him as well because I think 3 world titles would be a much more impressive resume than 2 OWYYC and 1 world title.
In the tier below the Big 5 I’d have Gentry Stein, Shion Araya, Yuuki Spencer, Sora Ishikawa, Hank Freeman, Shu Takada, Takuma Yamamoto, and Tsubasa Onishi
