Certainly, I get the frustration with Clay's lack of durability. I prefer durability too.
That said, a 'half year' pitcher can end up being a blessing in disguise. If the pitcher is healthy for the first half of the season, sometimes that's just enough time to give a youngster in AAA before he's ready to be called up.
If the pitcher gets injured midseason, sometimes they come back in August or September, healthy and well rested, and provide a much needed boost to the team. Injured players coming back later in the season are sometimes the best 'trade deadline acquisitions'.
These are not the kinds of things you plan for or hope for, but there is still some very good value from having a good player for half a season.