I mean, would you say modern Italian culture is the same as Roman culture? Devoid of context, the idea that your civilization evolves over time isn't a bad one from a fluff standpoint, and, as another user mentioned, it increases the likelihood of niche or late-game specific civs getting play, so I can see mechanical benefit too.

That being said, if anyone said the execution fell flat, I've no reason to doubt them.

I mean, actual civilization isn't a monolithic culture lasting 5000 years.

The issue isn't the premise. Humankind works with the exact same premise, and that's a great 4X. I'd definitely argue it's better than Civ 7. The issue was the execution.