The idea that the calories you take in through your mouth are the "input" and that the exercise you do to burn them is "output" and that the balance between the two is all that matters is bullshit.

Well, if you manage to consistently gain weight while consuming fewer calories than you expend, this has interesting consequences for thermodynamics.

It's not bullshit, but it's also a red herring for the actual question, which is how to actually reduce body weight in a sustainable, healthy manner.