I've been saying this for ages and I will never be tired repeating it: he's the Konohamaru of One Piece.
Period
Konohamaru was just Naruto fanboy from his village, he was never meant to have a bigger role, he wasn't pushed into big events, wasn't a part of and important faction (and even more important secret faction within that faction), wasn't trained by one of the strongest characters and was also an 8 yo kid.
Did you read Marineford? My god. How hard is it to read a children's manga?
And what did Koby do at Marineford and how was it significant for his character or the story? Please enlighten me.
Luffy's garp. Yeah, i know it sounds like a joke but it's true
Garp wasn't Roger's fanboy. He was actively chasing him, they have fought multiple times and ended up in situations when they had to work together, which led to him growing a huge respect towards Roger and vice versa. There is another character who parallels exactly that type of development with Luffy and you all know who he is.
Current Luffy no-diffs current Coby with his hands tied behind the back and a blindfold on.
Exactly. And people expect him to beat Hancock...

If he had
any achievement so far, even the smallest win against some sub 150 mil. bounty pirate, I might accept and say he has a small chance with the help of plot armor and pis.
I don't care if he trained with Garp. Real combat experience, beating strong opponents and overcoming nearly impossible odds >>>>> training.