During those last 6 years, evolutions of each software were not comparable.
Zbrush’s evolution contained big features changing workflow speeding it up.
That is impossible not to acquire some, in 6 years.
But Blender literally acquired new essential abilities, each trimester.
( EEVEE, Grease Pencil 2, Voxel Remeshing, Sculpt mode refactor, Geometry Nodes, Asset Browser, Color Attributes painting, New Hair )
Of course, you work a lot faster in Blender 3.6 than in Blender 2.79.
Were changes between Zbrush 2023 and Zbrush 2018 as essential that same amount of speed was gained ?
If your answer is no, you have to concede that gap between the two pieces of software was reduced.
That statement was not correct in 2017, anyways.
In 2.79, the skin modifier was already allowing to obtain quickly a base body shape.
There were addons distributing metaballs or Bsurfaces addon allowing to quickly obtain a surface from Grease Pencil Strokes.
And there was already Dyntopo.
Since 3.6, we have an asset bundle of Base Meshes.
The weakness of Blender was not in first steps of workflow, it was (and still is) in middle and last ones.
But it is true that there are essential things, that are still missing or complicated in Blender, while they are present or easy in Zbrush.
You just need to read The Big Blender Sculpt Mode Thread.
There are the recurrent requests made in it about certain brushes (Polish, Insert mesh), custom symmetry, multires reliability, sculpting layers, more retopology tools, better automated remeshing algorithms, painting, baking, …