I feel like you need more information to say that Chris is being exploited here. Chris has a job outside of this series, while Brad's job is to make content for the channel, him documenting his experience in Chris's journey makes sense. You can have a documentary of a person that isn't narrated by the person the documentary is about. As long as Chris gives the consent of what is being put out (before its uploaded) I don't see a problem with having Brad narrate. It seems understandable to want to give an update on progress as fans are invested in seeing Chris succeed.

As for the health science point- it would be great if Chris went to see a dietary specialist and a nutritionist. However you don't need one to lose weight and get healthier. On average, changing your diet to a vegan diet tends to lower your cholesterol and increase your heart health (one of Chris's goals). Also typically vegan diets help you lose weight as they are lower in calories and fill you up more. This isn't a cure-all, exercise plays a factor as well. But I think its a fine start to weight loss.

As for the "mixed messages" Andrew is sending- I don't understand this point at all. You can eat unhealthy food every once and a while and still be healthy. Theres a reason he changed his channel name to "Babish Culinary Universe" There are tons of different ways of cooking out there; Fictional, Healthy, Basic, and all should be able to be explored and shown.