Cubans still drive cars from the fifties. Nobody stopped them from importing cars. Americans do that all the time. Restrictions on real estate sales (You need a license to live in Havana) restrict the mobility of the population. A mobile labor force is critical to a modern economy, and restricting where people can live reduces their mobility and hurts an economy. They've also had to deal with food rationing and lack of transportation, although this was alleviated with the addition of more private markets and private taxis. Thus, the only small successes they had came from capitalism. Castro Cuba's lack of freedom destroyed the economy, not inability to trade with America.
The greatest evidence of this is the fantastic success of Cuban-Americans. Cuban-Americans started as refugees, but formed a thriving community in South Florida. Their descendants have found success that exceeds the average American. Cubans living in a free society perform brilliantly. Cubans living under the repressive Castro regime struggle. The conclusion is obvious; responsibility for Cuba's failure rests with Castro, not with America.
It is typical of third world douchebag dictators to attempt to redirect blame to external actors. They run their economies into the ground and blame U/S "imperialism" to cover for their own ineptitude. For Americans, this is both amusing and infuriating. The amusing part is that the "wise grandfather" of Hugo Chavez and Evo Morales had a little temper tantrum and lashed out at us rather than admit his own mistakes. The infuriating part is that we know there are still left-wing ignoramuses who will believe him.
The real reason Cubans have suffered is that they are reaping what Fidel Castro sowed. Although there were minor capitalist reforms, the system remains communist, which has always resulted in disaster. Cuba has suffered because of communism, not because of the embargo. The only reason Castro's policies didn't lead to ruin sooner was "sugar daddy" nations like the U.S.S.R. and Venezuela who kept him afloat. But these nations suffered because of their leftist policies, and now those wells have dried up. Cuba is in desperate straits because Fidel ran it into the ground. If anyone owes the Cubans, it's him. Perhaps he should turn over all of his accumulated wealth, which is almost a billion dollars.
I don't really expect Castro to turn over his money. I don't expect him to change his mind and accept that capitalism was always the wave of the future, not communism as his pal Kruschev thought. Castro has entered his "crazy old man off his meds" phase. It's annoying to hear someone spewing old communist canards, even while enjoying a lavish lifestyle that communists are supposed to hate. But I take comfort in the fact that eventually he'll die of natural causes the same way his ideology did.