If we all evolved from something why aren't we all the same?

What I mean to say is, wouldn't the most adaptable creature take center stage and eventually overtake everything else, especially over the course of millions of years? Why are there thousands of different types of birds, when by evolution only a few species should be superior and therefore exist. Could evolution simply be the evolution of a creator's IDEA of what does and doesn't work? Why are things so interdependent when by evolution we should just overcome all our flaws until we are perfect independent creatures?