There are definite philosophical questions over the merits of adding noise, but the problem with their example here is their denoising process appears to excessively blur everything, so both it and the synthesized grain image look noticeably less sharp than the source. The grain itself also looks too much like basic noise, and not really grain like.
that's an understatement. it just looks like RGB noise effect was added. film grain does not look like RGB noise. to me, film grain is only one part of what gave film the film look. the way the highlights bloom rather than clip. it also was more natural/organic/some descriptive other than the ultrasharp of modern digital acquisition. using some SoftFX or Black Mist type filters help, but it's just not the same as it is a digital vs analog type of acquisition. all of these attempts at making something look like it's not just keep falling down in the same ways. but hey, there's a cool tech blog about it this time. film grain filters have been around for a long time, yet people just don't care for them. even in Blu-ray time frame, there was attempts at removing the grain in the encode and applying it in playback. Netflix isn't coming up with anything new, and apparently nothing exciting either based on the results.