And then I'd remind them that they could have just dashed normally.
Moreover, how do the new rules close the "exploit"? You can still move 30ft while carrying someone. (60/2 - 30 vs 60 - 30*2) How is that difference meaningful in this case?
(Also, wouldn't you need something like rogue's dash-as-a-bonus -action to grapple and dash on the same turn?)
The article is pretty interesting overall but this example mystifies me. Am I missing something obvious?