I think they were trying to say that even if it were twice as efficient and everyone benchmarked it as twice as efficient, it still wouldn't make a difference b

I think they were trying to say that even if it were twice as efficient and everyone benchmarked it as twice as efficient, it still wouldn't make a difference because the Google devs are biased towards AVIF. It wasn't arguing that JXL is twice as efficient. It was just arguing that even if it were twice as efficient, it wouldn't matter.