This seems both very clear, and so obviously wrong that I must have misunderstood.
Are we really saying that ext4 commits metadata changes to disk (potentially a long time) before committing the corresponding data change?
That surely can't be right. Why on earth would you write metadata describing something which you know doesn't exist yet - and may never exist? Especially when the existing metadata describes something that does.
Perhaps what we're really saying is that ext4 does them in the correct order, but doesn't use barriers by default and hence they sometimes get written by the device in the wrong order? That would make more sense at least.