Honestly mate, you may be an example of what the article is talking about. As other people here have pointed out, the decline in reading skills begins with television not the smartphone. Same for the shorter sentences which make you find Dickens so hard.
I am particularly a fan of "flakes of soot in it as big as full-grown snowflakes—gone into mourning, one might imagine, for the death of the sun."
But even as somebody who likes Dickens' prose, I think his syntax is often a lot more complicated than it needs to be. In that sense I agree that it's slightly difficult at times.
Not "difficult" as in "this really took me a tremendous amount of effort to understand" but difficult as in "I think his syntax is a little more difficult than it needs to be."
(Of course, any sort of art should be understood in context. It wouldn't be reasonable to impose modern expectations on something written 150 years ago)