As entertaining and enjoyable as the play is, the book is far superior. The story is quite a bit different (and some of your criticisms aren't even found in the original material) and it's VERY adult and VERY dirty/raunchy. Definitely not made for children.
Not sure if you realize this, but the musical is actually based on Gregory Maguire's novel "Wicked" and not particularly on Baum's books. It is also a considerably tamed version of his book which is primarily sex, violence, and politics in the story of the Witch or as he names her, Elphaba, from Baum's initials. If you're going to read anything for this particularly story to find he references and reasons , read this rather than the Skottie Young books (though they are great).