The primary advantage of the US is cultural. It is not just the anomalously high risk tolerance and wealth, but people who attempt audacious goals tend to be celebrated. Americans shed the Tall Poppy Syndrome that is a very visible feature of virtually all other European cultures, perhaps because the US was predominantly settled by "tall poppies".
After years of working in various parts of Europe, I think it distills down to this. Sufficient talent, desire, and capital exists in Europe -- it is missing no ingredients -- but society there pervasively and subtly undermines anyone who dreams of attempting something really bold. It is a shame.