sorry if my approach seems a little simplistic, but that's how I see it. If we can work off foundations (Michelson-morley experiment, the speed of light is constant for all observers) and derive an expression for something else, I'm perfectly satisfied with it. I haven't just rope learnt the lorentz transformations, but I can't think of a better way to explain it. A constant speed of light AUTOMATICALLY results in relativity, as indicated by the transformation formulae