Of course having the world's largest economy next door and not trading with it is going to hurt massively.
But, as I said, this was a 60+ year process. Cuba chose a path: the path of state enterprise and dependency on Soviet subsidies. When that fell on its arse, reality hit them until they had a renaissance... with Chaves' Venezuela bankrolling them. When sponsored, they were "bravely beating the embargo". When the sponsors withdrew, they were "victims of the embargo".
The fundamental problem is not the embargo but going down the rabbit hole of shunning capitalism and free markets and instead pinning expectations on "allies" which, in turn, make them focus their efforts and resources on all the wrong things. Venezuelans have a similar take on their so-called "allies", they see them as leeches which systematically misuse and misappropriate resources because they are on a political quest, over and above an economic one.
Cuba are just not competitive and that's largely their government's own doing, the cummulative effect of over 60 years of poor decision-making. As I mentioned -and I keep coming back to this because it's a fecking island- Cuba's fishing industry is producing less than 10% of what it produced in the 80s. Their (state) fleet is literally what's left of what they had back then. It's not the embargo that forced them to stop reinvesting, producing and exporting to the many countries that happily trade with them. No, it's the fact they were inefficient but the USSR papered over those cracks.
The entire system and operating logic is fundamentally flawed, with or without an embargo. Obviously starker with one, more so when you see how China managed to pull themselves out of a hole by embracing free-market dynamics. It would be fair to say Cuba didn't have that path on offer, sure, but nothing in their rhetoric or how they've gone about things indicates they would have done anything remotely similar. In fact, I'd argue the government there welcomes the embargo as a convenient excuse with a galvanising effect they happily indulge in leveraving.