Not only can you have your first two functions equally developed, it is so common, Jung's colleague Marie-Louise von Franz resorted to typing people after she and the client felt they had figured out the INFERIOR function. It was her trademark, so to speak, typing people in that manner since it was nearly impossible to ascertain a person's Dominant function due to its likelihood of being confused with the Aux function.
"Many people, moreover, develop two superior functions so well that is very difficult to say whether the person is a thinking-intuitive type or an intuitive type with good thinking. But does the intuitive-thinking person suffer more from banging his head on sensation facts, or from feeling problems? Here you can decide which is the first and which is the well-developed second function." (Lectures on Jung's Typology p.21.)