Boa turned all marines to stone except koby. Fact
Which means it failed to work on him or he dodged every single one of her arrows. Fact
Bbs men were shown turned to stone. Fact.
Koby is the youngest marine to even have a seraphim chip. Fact
Even though he is a member of sword which means he should get anything of special not from the world government he was still given a seraphim chip like the vice admiral that was deployed with him. Fact.
Don't know what you talking about
Coby isn't even VA level.
He's a young and promising member of sword, who has Garp's blessing, that's it.
Of course he'll become an admiral in the end, but that's several years into the future (epilogue).
It's just so plain obvious that he has no business competing with the top dogs as of right now. Oda made that abundantly clear on Amazon Lily and Hachinosu.
He's basically pre-skip Luffy right now and if I had to take a guess, that's what Oda was going for all along with his two-sides-of-the-same-coin approach.