Trying to keep my reasoning succinct in order to avoid writing a wall of text:
The soviets were geographically blocked from this being an option
Similarly for Vietnam for different reasons
Cuba doesn’t have the option of dedicating the requisite amount resources(and has the misfortune of being an island next to the most powerful current naval power)
China has the geography to become a great naval power. Sure, it doesn’t have both coasts. It has land connections that led to the Silk Road being a thing on the other, possibly a greater advantage.
They are building up militarily, and seem to be advancing commercial maritime pursuits on this well.
Thoughts?
I was under the impression the USSR had a very respectable navy by the 80s. They just didn't have the time or resources to make a world class one in the 20s and 30s for WW2, whereas China will have a powerful navy in time for WW3.
edit: Also the Soviet Navy did have some interesting things that the US didn't have like nuclear powered missile cruisers and titanium submarines
In terms of submarines they probably(definitely did at certain points) lead the world. Knowing their missile technology they probably did have better missile cruisers by virtue of better missiles. The strength of a navy is its ability to project force, while subs and cruisers are critical to a peer on peer conflict they don’t project well.