The output by stream is obviously slower than fs.writeFile().
Nevertheless, stream is powerful because memory control by highWaterMark can prevent memory from being consumed too much at once.
However, this can not be realized with just Writable alone (at least Readable or Generator is almost required), you can ignore it, but in that case no memory control will be done and the stream loses its maximum advantage.
Although it is possible to use JSONStream.stringnify(), it is said that an issue has been posted, "It is 100 times slower than JSON.sringnify()".