Aw, your poor kiddo. I hope he feels better very, very soon!
I think you can go either way and have great results, and feel good about it.
If you do really *want* to homecook though - then you just have to truly make sure it's balanced properly vie balanceit.com or something.
If you choose to go w/ Science Diet - be confident in it, and know you're choosing something that is tailored to a specific problem - which is best for your little darling.