I still don't get why you need the horizontal cut at all. The diagram at the bottom of the blog post shows how unnecessary it is when you do the vertical cuts at a narrow range of angles like that (which I have been doing for a while now).

The point of Kenji's method (really, all radial-ish methods, but radial is strictly worse) is that you don't have to do the horizontal slice. If you slice vertically, you do --- you can see it for yourself, if you don't the dice from the edges of the onion are almost twice as big as the diece from the center.

I’m sure I’ve seen a clip of some tv chef saying it is unnecessary. Maybe Jacques Pépin but not sure.