I've had full diamond 3 times (Mars mission, Zone 85, Survival games 6) I've lost in full diamond... (2nd on zone 85) I've killed players in full diamond (no statistic XD) Armor doesn't really matter when you have TNT, bows, golden apples, enchants, and many other strategic things. Then there's your computer, is it fast is it slow; Is your ping good; is your fps high. Full diamond isn't overpowered, because strategy, skill, Outcome, and speed are how players win Survival Games.
EDIT: Oh and best gear Sharpness 2 diamond sword, Protection Iron chest and Legs, Proj Prot Helm and boots, 1 Potion of Speed2 and 1 potion of Regen.