All 4 have the same insecurity
The insecurity of being a burden to the crew and not being good enough
Luffy honestly is rarely insecure about his strength the main times he was when he was a child, sabaody, post marineford were all moments where he didn’t feel like he was good enough. The ones later in life making him question if he’s worthy of his crew and becoming pirate king His childhood being a big reason he’s so tough on character like shirahoshi and momonosuke since they remind him of himself back then
At this point I’d say he’s fine and pretty much over it
Usopp while obviously not the strongest strawhat is also pretty much grown for the better. It being very much highlighted pre timeskip that for a lot of it Usopp started to feel unworthy and not good enough to be with the crew. That coming to the forefront during enies lobby
Now he’s excepted him not being as strong as zoro or sanji he can still contribute in ways they can’t and be just as valuable. Also realizing that luffy doesn’t pick members just because they’re strong but because he likes them. So while he’s not usually going to be in front of all the action that doesn’t mean he’s not willing to do whatever he can to help and sup
Sanji is/was an extremely self sacrificing character. Always ready to put the wants and needs of the people he cares about above his own. Because of that he so willing to give up just about anything even his life away easily if he believes it helps them. Even the thought of disappointing the people he cares about weighs heavily on him
And sanji himself realizes he has a lot of “flaws” and “weaknesses” that he himself is willing to carry his own plus more he was very much ashamed to get help for the things he can’t do. Him never wanting to feel like a burden on anyone else
All that getting very much highlighted during zou/wci. With him showing growth for the better since
It’s the same with zoro. While confident in his strength he constantly dogs on himself about being to weak and how every failure is because he’s not good enough. Even when the situation isn’t even really his fault
With Zoro always trying to come off as strong even when he doesn’t need to. To the point he can come off as extremely cold despite not actually meaning what he says. Zou being a clear example of him saying 1 thing but deep down meaning the other. Punk hazard being another example of him being extremely hard on himself that he projects it out.
The comment about Vegapunks death could also be a scenario of while there might be a bit of truth in what he says a lot of it could just be him projecting his insecurity of the situation and everything that happened in egghead
Say what you want about egghead zoro even if you think he did the best and was the mvp you still gotta admit man was getting shit on verbally. Just about every character friend and foe taking a turn basically calling him incompetent. Not saying I agree but it’s just what happened.
With zoro being hard on himself as is with no help needed I imagine he feels way fucking worse. So hopefully oda can delve more into that aspect of his character. I know people don’t expect much meaningful character moments and growth for zoro anymore but I still do so eh.