You’re talking about the application of labels, not shaping a definition. What’s the linguistically prescriptive definition of communism that’s descriptive of these regimes?
If most people think I’m straight, but I’m enjoying getting railed by 10 dudes 10 times per day, I’m not straight - they’re wrong. If everyone agrees that getting railed by 10 dudes 10 times per day is straight, that’s prescriptivism descriptivism.