Not necessarily, you can dehydrate foods yourself. In fact, they are an important aspect of prepping. The main issue is fat can't be dehydrated. It goes rancid. That means you cannot live on dehydrated food solely. You could however make up meals as the base of a dish and then add to it. Example: make a stew this way, but add jerky and some oil to get the necessary fat. A lot of people buy frozen food and then the food is prechopped up and so makes prep time shorter for dehydrating it. It comes on sale and you then buy and dehydrate then, much as you would from the garden as it comes in.

A prolific youtube prepper went on an extended camping trip and ate all dehydrated food and felt the drop in calories. It packs very light, so if you use it for that reason, take some oil along.