But seriously, did they think this through? 70,000 miles for 349 Euros? At about half a cent per mile, that almost seems too good to be true. And bear in mind that these can also be redeemed for flights in F. Is there a limit for the number of passes that you can buy? I don't see one...
I think they thought it thru pretty well. With 70k miles you can do virtually nothing! Buying Y class tickets with taxes excluded you come to the same price or even a higher one than buying it using cash only which in addition would earn you miles.
For the cheapest C class ticket you need at least 10k additional miles, and as it was already said, the availability is somehow limited (e.g. march 2015 was still good as I checked a few days ago)