As of now, this is the best option amongst options. Hall is not ready to start and should be converted to relief in my opinion, and Rodriguez pitched last night and while his numbers have been decent, he's still struggling to throw quality strikes in AAA. Denoyer has regressed, Povich is going through a tough period and can show flashes his brilliance along with the inability to throw enough quality strikes (sound familiar?), and McDermott is still AA (needs to be promoted but also struggles to throw consistent quality strikes at times.
I think we're also seeing the downside of drafting almost exclusively hitters in the first ten rounds. Not a lot of teams want to trade upper level pitching prospects who look good for hitting prospects.
So yes, right now, Irvin, who was acquired for Darrell Hernaiz, is probably the best option as the #5 starter. If he can get back to where he was last year with Oakland, he should be fine in that role.