I half-agree with this. People occasionally argue that, e.g., Rust won't be suitable for production use until it has two fully independent mature implementations, and I consider this a silly requirement that doesn't serve any real purpose. On the other hand, once multiple separate implementations are already in widespread use, there's immense value in working out a least common denominator of language features and standard library APIs that work everywhere, so that library authors can write portable code that users of any implementation can depend on.

Of course, it's always possible that the standardization body doesn't in practice do a very good job, as seems to maybe be the case with the C++ committee. Also, I'm only talking here about technical considerations, not governance ones.