This feels a bit dramatic...not even talking upside, I think we're at least talking about 3 guys that sit somewhere between 3 and 4, and even that's a debatably low ranking. They aren't great, but Tillman, Gonzo and Jiminez are not 3 #5 starters...
We're having a definition disagreement.
Take a guy that performed like Mike Wright last year (6.04 ERA). Should you consider a guy like that a #5 starter? I propose a guy like that belongs in AAA and therefore isn't a #5. You can't seriously tell me that you'd be happy with a guy like that in the rotation to start the year (although given the realities of attrition, it would be reasonable to expect him to receive a few starts especially presuming decent results in the minors). Others would argue that he is a #5 starter because that's the worst possible.
I propose a #5 starter is the worst possible guy that you'd still be comfortable having in your rotation. You'd be happy to replace him if possible, but you wouldn't be upset to see him there. Although, you may not be happy with three of them.
I insist on using my definition because I feel it adds necessary nuance to the discussion.