The focus is all on Luffy because Oda is rushing to finish the series. It's very simple. It is unfortunate but you can't blame him for that.
Then why does he create dozens of shallow side characters that nobody Cares about and building repetitive useless plotlines for them (like helping a misérable kid/girl...)
I think that this is a huuuuge flaw in Oda writing, hé loves creating characters (or lets Say drawing characters), those characters waste panel Time, nobody gives a Fuck about them, and the next arc we already forget their James because they left 0 impression on us.
Then there is this weird writing technique that I think was invented by Oda himself during pH: making SH run pointlessly during dozens of chapters just cause Oda is too lazy to find something todo with them.
Then instead of developing SH, he turned the two girls Into sex toys(especially Nami), and the rest (apart from Sanji and zoro) Into marginal characters. I mean, do you remember that there is a SH named Brook? Lool, sometimes I comoletely forget about him since he got nothing todo in this arc.
Then he focuses on Luffy alot post timeskip but the problm here is that Luffy doesnt get any character development at all cause he is a poor character since Time skip and I am afraid hé will Always be. When he Gets defeated, he screams meaaat and comes back, or just gets a random PU like a gift from haven. Its like if Oda is trying to show us that if you are dumb, arrogant, and lucky, you Can get an army of cheerleaders and become PK.