Getting to a healthy weight is more about nutrition than exercise. Tennis is a good sport to burn calories, probably better than running; but you do risk injuries with the extra weight. This is true with running too - but you also risk overuse injuries with running, even if you aren't overweight.
Agree. But most people getting healthy work on their diet even if its by luck. For example if you just hit the gym you sorta don't even want to eat a twinkie because you fear all you work will be undone. (And you would be right haha).