No it isn't. I can buy a 3TB hard drive that will last for at least the next five years for like $100. Dropbox charges $10/month for only 100GB of space, which works out to 1/30th the space at $600 for five years. With a hard drive, I always have access to my data, even if my internet connection goes out or I am in a location without a connection.
<cynicism>Hard drives are guaranteed to not fail for at least 5 years? News to me. Even ignoring premature failure, most warranties these days are 1-3 years.</cynicism>
On the other hand, assuming you've got local backups, I mostly agree with you.