Power to weight ratio was the supreme problem for early flights. People like Cayley had already invented the concept (and even the form) of the aeroplane before any powered flights, and given a sufficiently powerful/light engine his designs probably would have worked.
Once the Internal Combustion engine had been invented (as a result of several significant steps by different people) powered flight was inevitable.
I think this reasoning is pretty much accepted generally, with practical European aero-engines being seen to be largely dominating and driving aviation development from around 1906 with the Antoinette through Gnome ( 1909) until well up to the end of WW1.