People tend to lose weight from dieting, not exercise. Unless you're training for a marathon or something, even vigorous exercise tends to burn so few calories that an hour at the gym can be erased with a single trip to McDonald's.

Probably accurate. The amount of exercise needed for effect is less than a hour per day (less than 30 minutes if intensive) but this is a not done by most.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5556592/

https://www.cdc.gov/nchs/fastats/exercise.htm