Context. It's important to have blood glucose readings before you give any insulin and then some readings after you give insulin so you know what sort of an impact a particular dose is having for your cat.
One hour after Prozinc injection will probably not show much of a change. It takes time for any insulin to start working and show it's effects. You also want to have some idea of the nadir or low point in the insulin cycle to help you know what type of adjustments you should make in the dose. That low or nadir varies with each cat. It's why one of our mantras here is ECID or Every Cat Is Different. It's one reason we are such strong advocates for home testing.
We strongly recommend that you are home testing before you make a diet change, like switching entirely to wet food. When I was switching Wink from dry to wet, there were dramatic changes in his BG levels that required changes in the dose.
If you are home testing, you can monitor these BG levels and help keep your kitty safer.
I would not drop the dry food entirely at this point unless you also drop the insulin dose dramatically.