[pandaman]

>An hour of fairly vigorous cardio every day will give you what, 3-400 kcals of extra calories to play around?

This depends on your VO2max/FTP. At very modest 150W FTP it would be ~550 kcal.

> Something you can easily overcome by eating a donut

Don't eat a donut then? It's not like donuts randomly fly into your mouth and you have no control.

>Exercise is absolutely useless for weight loss if it isn't coupled with a controlled diet.

That's obvious. It's not "absolutely" useless as it will take much more effort to gorge on food (e.g. I don't know anyone who would be able to eat a donut after an hour of a vigorous exercise, least crave one) and you also have less time to stuff your face and think of snacks. But it's entirely possible to still overeat while exercising.