I think the comparison of tangs with triggerfish ist not the best choice because the following possibility is not especially contradictionary. Tangs need larger tanks than angelfish but several triggerfish genera (Odonus, Melichthys) need at least as much space for swimming than Acanthurus tangs.
Obviously most reef aquarists think of low quality (freshwater?) flake foods when thinking for flake Food, but there are flake and granular foods that fulfil all physiological needs of most reef fish to stay healthy. Critical is the proportion and quality of oils with PUFA.