Let me try again. I didn't say having a multitude of native languages prevents development. I said it doesn't help. Especially today trying to play catch up.
Developing countries today don't really have the advantage of being able to pillage and plunder their way to the top with impunity.
But that's exactly the policy of the Chinese government you describe, we are not talking about a natural phenomenon here. The policy is to actively eradicate and erode other languages, and only want one language in the end.