A lot of people can do what the strawhat are doing.
Mihawk or any strong fighter can be acombattant
Any good cook can be a cook
Any carpenter can be the carpenter (in fact Iceberg is on the level of Franky it was clear in the story)
Anyone can be a helmsman
Anyone can be a look out
Anyone with a good aim can be a Shooter
Anyone can be a doctor, in fact Marco could easily replace Chopper
Pudding could replace Robin as a Poneglyph reader
We didn't met a lot of musician but this is again not that hard to do
Etc.
You see. Pretty much anyone can do the job of the strawhats, sometimes at the same level. That is why it is important to note that what makes a good strawhat, is how said strawhat can do his or her job in a very
SPECIFIC situation.
That is why I put so much emphasis on what I call the
Shining Nakama Action. I hope that one day you will read the story carefully and understand how this pattern is important. And if you want more explanation, again, there is an article
on my blog about it !