I believe that it's a team of four people, each with strengths and weaknesses who are on a common journey and have teamed up against the elements and a vengeful antagonist while on a journey to meet a common consultant.
I can't speak for Scarecrow and Lion, but in the book the tin man absolutely had prior business with the WWW that didn't end well.
All four of the travelers had a problem with no clear answer and were going to ask the Wizard who might have some sound advice. So it's a road trip for folks with a common destination
Also the flying monkeys were their own people and geased to obey the amulet, which WWW possessed.
Also, the solution really was the friends they made along the way. If I were Dorothy, I'd rather be there than Kansas.