My argument is simple, if you spend the same amount of time going uphill as you do on the flat, you will burn more calories going uphill generally. Of course, it is easier to do longer rides that are flat, thus overall you will probably burn more calories if you do a 4 hour flat ride than if you climb up Mount Ventoux in 2+ hours.

Quit trying to justify why you do certain things, and quit giving dodgy advice to others and just do what you enjoy and enjoy what you do.