I think Dessens was our best starter last year.I don't know if it makes much sense to take your best starter from last season(Reitsma) and make him a middle reliever.
But I agree with you that Reitsma should be a starter unless Williamson proves he can't handle the closer's role. Reitsma would be my second choice to close if Willy can't...in that case, they switch roles.
Also, I'm agreement with somehow dumping Castro (preferably) or Dawkins (get what you can now - he ain't gonna get any better riding the pine). Rijo, as incredible a story as his comeback has been, should also have to earn his spot on the team.