Genuinely, what do you think the term “shoulder to shoulder” means in the context? What could giants who believe all arguments end with a physical confrontation of might mean when comparing three characters? Is it that Gabans Legend is as great as the Pirate Kings? Is it that the three have equal standing on the ship like how it was used for Arlong/Jinbe and Shanks/Buggy?
Or most simply, was it just odas way to point out the power of the three top Roger pirates. After all, Oda pointed out that Ray and Gaban were already stronger than Oden earlier in that speech.
It's simple really, would you say Sakura stood shoulder to shoulder with Naruto and Sasuke vs Kaguya? Absolutely.
Would you say the legendary sannin stood shoulder to shoulder together? Of course.
Does it have strength implications? Absolutely, it means that they are significantly stronger than everyone else in their respective groups that isn't included in their sub-group, e.g. - the sannin were above every other leaf shinobi at the time, the rooftop 5 stood shoulder to shoulder against the 2 Yonko and they were the 5 strongest supernova etc...
But it doesn't mean the individuals in the sub-group are close in strength. Relative in the sense that they collectively shit on everyone else, not in the sense that they're on par with each other.
E.g. - the SHs have had the M3 since forever. Luffy has been able to absolutely bodybag Sanji at times - even as far back as vs Arlong who was high-diffed by Luffy yet was utterly unimpressed by Sanji. And still, they are known as the Monster Trio - not because they were on par with each other; Sanji has never been on par with Luffy. But because they were vastly superior to everyone else, e.g. - on Saboady pre-TS, Luffy made sure when they split into 3 groups, that each group had one of the M3. Because these three are the protectors of the crew and the main fighting force of the SHs. Just as Roger, Rayleigh and Gaban were the legendary main fighting force of the Roger Pirates.
