Socialism has never been fully realized, as under communism the surplus and means of production were controlled by the state, not the workers. It was state capitalism.
If you see socialism as only some kind of state where capitalism no longer exists, then sure, we've never gotten there. Probably never will. Hell, even if post-scarcity communism is someday realized, it is equally possible that we got there by way of capitalism. Just because someone theorized that capitalists would put up roadblocks on the way to post-scarcity doesn't necessarily mean they would or that they couldn't be overcome.