That's such a typical straw-man argument. Firstly nobody with the right mind will say "garbage in, garbage out" is all there is to producing good code. Knowing principle doesn't automatically helps you solve the problem. It's like saying I know programming but why aren't I a successful tech company billionaire? Knowing the principle gives your a solid start, it doesn't guarantee your eventual success
Similarly, CICO is just an simple scientific fact to give you the idea what's happening physical world. Did anyone say CI and CO calculation is simple? Are you seriously telling me your could gain weight when you just eat air?
Tell me just one dieting method is simple, effective, helps everyone 100% to achieve the target weight again? As I mentioned in the above post, a good recipe doesn't make you a successful cook. You are not going to become Gordon Ramsay by watching his video alone