No, it’s not. Not always. When you get into restaurant finance (something I’ve dabbled in a little bit during my professional accounting career), it’s pretty common for pre-made items to be more expensive than fresh, even after accounting for labor. And fresh is almost always going to be better quality.
While you might be able to pinch a few pennies in food prep, much of the time the longer term health of the restaurant is best served by using better ingredients and spending a bit of time (and therefore money) on labor. You get dishes you can charge more for and food that people keep coming back for. And that generates long-term profits, rather than profits for this week and little return business for next week.