That's the correct answer. You can't exercise your way out of a high calorie, high sugar diet, unless you're willing to dedicate several hours per day to intense exercise. Normal exercise is an atrocious approach to countering high calorie intake, it simply can't work. You can work out for an hour, and one soda wipes it out entirely, or a couple slices of pizza.
No, the problem is and will remain dietary in nature. Americans could stop all exercise across the board, change their diets, and lose massive amounts of weight trivially, just by cutting out a few common items that nearly all obese Americans over-consume. I've yet to meet an obese American whose diet I couldn't trivially radically alter by just removing a few particularly horrible things (eg sugary drinks, ice cream, pasta/pizza, high sugar snack goods). People think they have to change everything about what they eat and go to the gym five times per week to drop weight, and that's entirely false, all they have to do is eliminate or dramatically reduce the couple worst items in their diet and that's usually enough (it's rare that there are dozens of villains in their diet that matter, it's almost always just a few items that are doing 3/4+ of the damage).