When Gary Taubes surveyed the literature to find the evidence that exercise is useful for losing weight, what he found is that the scientific literature itself proves this statement is either not true or even slightly false. There aren't any studies where exercise has lead to persistent, significant (which I would define as taking someone from clinically obese to normal weight, not merely shaving 3% off of someone clinically obese) weight loss without a diet change. I have not seen any evidence to the contrary, I am not aware of any evidence that exercise on its own actually works for weight loss, let alone that exercise can wipe away making your diet even worse.
He also observes that it is pretty rare for people in practice to get serious about exercise, but leave their diet completely unchanged. If you start exercising consistently and cut out sugary soft drinks and lay off the potato chips, how you do know which thing did what?