First: In these posts, I've treated the Rosary in a very utilitarian fashion. Meditate on the life, death, and resurrection of Jesus Christ, I've been saying, and you could wind up less lazy. Substitute "the Rosary" with "fifteen minutes of sitting in a chair with a Bible on your head," and the arguments are basically unchanged.
So let me add that, though doing a lousy job praying the Rosary may still be a remedy for sloth, no one should settle for doing a lousy job praying the Rosary. Then, too, I don't believe it's even possible to pray the Rosary every day without improving in all sorts of non-sloth-related ways.
Second: If someone is slothful, why would he resolve to pray the Rosary daily in the first place? All five posts are concerned with what could happen to people who may not even exist. To this, I'd say I have in mind the sort of person who knows he's slothful, who sort of wishes he weren't, and who's looking for some [easy, of course] way to do something about it.