There is no one stop shopping in the fitness world. I believe in mixing it up, yes functional training has its place along with all of the other amazing creative ways to workout.
If a trainer is true to his or her client, the program design will fit the needs of the client.
Establishing a strong base and foundation along with being specific will help you decide what modality will best work for your client.
Also, there is no one size fits all training, it’s called “personal” for a reason!