So great you found a food that is working. I think most of the vet script foods as "last resport" trials, mostly because there is such poor nutrition in them and most dogs don't like them.
If there is a reluctance to eat in the morning, that may be signs of trouble brewing (might not be). You might try some probiotics like the mercola pet probiotics in the evening, which often helps a stomach that isn't quite right.
I use the K9 natural tripe. Jazz will only eat the freeze dried (as opposed to frozen or canned), but it was a turning point in her IBD. I've been meaning to try the raw someday.
Again, I don't think this is picky for the sake of picky. I think this is picky because things aren't optimal. How not optimal depends on the sensitivity of the dog. Some dogs will stop eating sooner than others. Other donkt stop eating if there are other dogs/cats in the house. I definitely wouldn't let that go on for a week, but you are learning what is going on with your dog AND also when to trust your instinct over yout vet's.