Marketing should come first? What are you going to market if you don't have anything to sell?
Agree to sell the "air" filed in the "beautiful wrapper", i.e. with good marketing is quite possible, but to sell the most ideal product with very bad marketing is unreal ...
Of course, if marketing is not done qualitatively, then its not realistic to sell anything, for just people will not even enter, it doesnt depend on your ideas or even