I’d say the major thing is the amount oda has made sure to separate shamrock from all other Holy Knights.
1. He’s shown to have special privileges in his meeting with the gorosei “only cause it’s you”
2. He’s stated to be as strong as shanks would have been with the Deep seal (this version of shanks was already a powerhouse with CoC coating)
3. He’s given his very own demon ability like the gorosei in the form of Cerberus his sword
I think having him be limited by ranks is unfair to the visage of this character oda is building. It’s like limiting Garp for being merely a VA. So, since oda gave shamrock seemingly a similar kit as the gorosei (immortality, demon, and CoC) why would the fighter still in his prime be weaker than those who are far out of it and looked like subpar fighters last arc?
Fair you’ve been able to establish that Shamrock has been separated from the rest of the Holy Knights and I agree but that’s is understandable given he’s the captain of the Holy Knights (Lucci was much stronger than the rest of his Cp9 members pre-ts) but still not enough justification to put him over the Gorosei.
On the demon ability ting, there’s no evidence that is the same ability as the Gorosei but regardless of the logistics of that Shamrock has a deep seal not an abyss seal which the gorosei have until confirmed otherwise and also those seal ranks exist for a reason.
You can’t just completely bypass all of that as it will only undermine it.
You’re basically discarding the Gorosei positions and all of the seal development Oda’s setup just coz you think Shamrock is the bees knees.
Now I’m not saying Shamrock will not eventually be as strong as the Gorosei when we finally get to see him strut his stuff but there is a procedure to that. He will need to be promoted like his father was for that to happen.
Way I think it’ll go personally is that Oda will put Shamrock in that sweet spot just under the gorosei with similar abilities but not quite the same.
For example, CoC coating like the Gorosei so will be able to defend against CoC users (except they will be stronger coz of their abyss seal and have other perks the abyss seal gives)
Anyways to summarize my point is that if Shamrock is what you think he is, he will be given the appropriate rank and abilities to justify it. Won’t just override ranks & abyss seal coz.
On the Garp example, it’s a false equivalence btw. Garp not only has the feats to back up his hype but was also offered position of Admiral.