@zensky We haven’t given much of anything away, don’t worry. :)
I love Fringe and I can see where you’re coming from, but I think that you’re really overthinking this and that this is mostly coincidence. The characters in The Wizard of Oz are all very clear archetypes, so it is only natural that the characters from Fringe have bits and pieces of each of those characters, as do most characters in existence. I don’t think that any one of them is definitively one of those characters. I think if you really analyze the characters you will see that they are surprisingly complex, even if they seem to match these archetypes on the surface.
I have to completely disagree with yours and @Imadethisupwithnoforethought‘s analyses. To start, one of my biggest problems with this whole concept is that Walter is so far from being any of these characters, especially the Tin Man. The Tin Man had no heart, but Walter is the most emotional and loving character in the show, and he chose heart over brain as opposed to having both. Walter’s personality and questionable sanity make him a very confusing and complex, and I don’t think he is even close to matching any character of the Wizard of Oz. If anyone, maybe Nina could be the Tin Man. But Olivia is not at all like Dorothy at all in my opinion. Personality wise, she is the most ambiguous of all, and her experiences do not align with Dorothy’s whatsoever. Viewers are not meant to fully understand her or be able to really identify with her, otherwise the show would be boring. It would make no sense for her to be at all related to Dorothy. Furthermore, Astrid is timid but not cowardly (and there is a big difference) as she has demonstrated several times during the show. As for Broyles, I do not think that his character has been developed even remotely enough one way or the other to assign him to a character, but I definitely don’t see him as the Scarecrow. The Scarecrow is a happy-go-lucky, no cares in the world type of guy, and Broyles is quite the opposite. However, I will say that I can certainly see Bell as the Wizard, and I do not think that this is a coincidence.
I do think that the show makes references to The Wizard of Oz to hint at a message or a common theme, but I don’t think that the characters are, as a whole, part of these subtle (or not-so-subtle) hints.