It's not clear to me whether your point is intended sarcastically, but for those who don't know, the Roman Empire was incredibly diverse throughout all of its history. Rome itself was a cosmopolitan urban center for centuries. Even after the split and collapse of the WRE, the east remained hugely diverse.
Not so much Rome as the entire Mediterranean has swapped genes and cultures a hundredfold for thousands of years being the trade hub between Europe, West Asia, and Africa.
I also feel like I'm reading a bunch of coded statements with some of these comments in here.
Oh yeah, I've found 'the reason why Rome collapsed' type arguments to be at this point mostly a kind of 'Rorschach Test' for the ideology of whoever is promoting it.
Honestly, I'd rather deal with the coded language visible thus far than have to explain why Diamond's Collapse is utter garbage for the hundredth time.