DHBC was a show about losing weight, with competition thrown in. TBL is a competition show: the weight loss is just a gimmick. That's the main difference. Discovery Health actually wanted to help people. NBC just wants ratings and drama.
They're presenting them with trainers who (from all indications) tell them WHAT to do, but not why. With tables full of food and (again from all indications) no guidance on what is good for you and what is not, and what appropriate portion sizes are, and how to determine how many calories might be in various things.
When presented with clear choices of right and wrong (the bake-off, the "temptation" fridges), the contestants know what to do and do it because they're motivated. But when the choice is less clear (meals), they don't always make the right choices because they're uninformed. If the show were actually about weight loss and helping these people, well, then it'd be DHBC, I guess.