The point is: being able to run a brain inside a computer is not the same as understanding that brain. If you wanted to build a new brain, you'd have to reach for the tool all the time in an iterative way and hope for the best. Only tools that aid in understanding matter. We have only very few tools that help DL researchers better understand what they are doing. Hence DL is more akin towards science than towards math/CS or engineering.
Given enough computing power, most theories could theoretically by proven or falsified purely through reasoning.