Castro is a ruthless despotic killer. The entire economy is under his thumb, most of the prosperous larger scale enterprises are run by the Army. He purposely forbade minor economic activity (i.e. shops, trades) that would normally form 1/2 of the entire economic base. Some of this has loosened up.
You can't blame a blockade for not having mechanics available to fix cars when being a mechanic is defacto outlawed.
If Cuban were an open economy, even with crappy authoritarian leadership and and embargo, it would probably prosper.
Trading with other nations has some 'essential' aspects, but mostly it's not necessary, it's just advantageous. And there's no reason to have to trade with any one nation, generally.
Cuba might need very specific equipment from in order to advance some parts of the economy - for example, many factories need equipment only made in Germany as one example, the same thing applies to US sourcing. This would be acquired through intermediaries.
But by and large, trade would come in commodities, tourism etc. none of which is 'essential' between US and Cuba.
Not having the US to trade with is a drag, but anything that Cuba would actually need (i.e. specialized tech) would be purchased through intermediaries.
Definitely foreign direct investment and tourism would hamper things, but not by some kind of existential amount.
Castro Inc. is 100% the problem there, that people continue to defend them in some way is astonishing and shameful frankly.
I think I know what case you're referring to, I think you're misrepresenting it.
It's pretty sad that people are defending Castro Inc.
I believe that hatred for one's local political opponents transcends any material reality which is why Castro still gets so much indirect support in the West. Or let's just say 'lack of condemnation' or 'redirection of blame'.
In this way, the 'points' that Leftist/Rightists can glean over their opponents, they will use by seriously distorting the facts over some 'example' entity like Cuba.
The ability to rise above that to me is the 'litmus test' for ideological inanity vs. true good faith reasoning.
So many people don't want to admit that Castro Inc. is a vile authoritarian murderous regime, an so they'll do quite a lot to cover that up, by highlighting the few supposed positives, and rarely covering the negatives.
This is the 'red flag' of intellectual failure and I pretty much ignore anything these people have to say, much like I don't have any time for people that think that Donald Trump is some kind of 'Glorious Businessman' and can't fathom that what he does on TV is just made up.
Castro was (now Castro Inc.) a tyrant in the most obvious and classical sense it's clear as day.
[1] https://foreignpolicy.com/2019/07/15/the-end-of-cubas-entrep...
And yes in practice. Cuba trades with China, Spain, Canada, Mexico, Brazil, Germany, Italy, and the Netherlands.
As far as the embargo I don't think you can really separate it. Countries with more oppressive dictatorships have been able to develop economically if given the chance to trade.
It would be the highest in central/south America alongside Chile.
Nature maagazine had a bit on their vaccine here [1]. It's not unreasonable or 'bad journalism' at the same time, it's biased towards them with no hard questions, making excuses, and soft-balling them questions on the embargo etc. and finally it doesn't address or put into context the overwhelmingly negative outcomes which are a result of the regimes power.
[1] https://www.nature.com/articles/d41586-021-01126-4