It's ok to disagree with the vet about food. Many members here have. Most cats don't miss dry food at all. For snacking, canned food can be left out. There are ways to keep canned food fresh all day.
Air dried raw and freeze dried raw are better "crunchy" options than dry food. A few low carb freeze dried treats daily may be enough to satisfy a cat's need for crunching.
For regular dry, Young Again Zero could be fed. It supposedly has zero carbs but that has been debated many times in the past here on FDMB. Some cats are super carb sensitive so you'll have to see how dry food affects blood glucose levels. I think you can only buy Young Again directly from the company web site.