The article has screenshots that very much demonstrate this difference. The first screenshot has, for example, a lot of POIs (statues, shops, theaters, viewpoints), highways that are different when they are bridges, different colors for grass vs parks, different line widths for different highways, sports fields, building and neighbourhood names, arrows denoting one-way streets, building parts, stairs, trees, and a lot more.
The second screenshot has none of that, aside from a single trolly station and a single street name (which is also rendered incorrectly).
I've tried a lot of vector styles (all openmaptiles styles, the base protomaps styles, all mapbox styles) and generators (protomaps, openmaptiles, mapbox). None of them come close to the amount of detail as the raster OSM tiles while still being as readable.
I've never found anyone as bothered with this as I am. Vector styles are cool as they zoom and pan very smoothly, and their style is fairly easily editable. But, for any map where you actually want to see map data instead of using it as a base map for your own data, vector maps fall short.
Maybe it is just because of computational limits. I can imagine that displaying the same amount of detail as the OSM raster tiles would require too many resources: both on the client side and for tile generation.
It would be nice if OpenStreetMap would try to mimic their raster style closer, instead of providing just another low contrast, low detail base map. I hope this release of open vector tiles will facilitate more detailed vector maps!