Todd Gilchrist editor Although it isn’t structured any differently from dozens of other cradle-to-grave documentaries about artistic luminaries, “Luther: Never Too Much” sheds light on much more than just the life and career of R&B singer Luther Vandross. Drawn largely from interview and performance footage of Vandross over his almost 40 years in entertainment, and bolstered and contextualized by retrospective talks will collaborators and confidantes, director Dawn Porter’s film exposes some uneasy truths about the music industry and the media we may now know, but whose seeming ubiquitousness at the time he was alive may be difficult to fully comprehend.