As the title states, when wearing diadem gear and entering a dungeon or instance which level syncs you down, none of the sub-stats from the gear is added. I have tested this many times in pvp and dungeons, by swapping pieces of diadem gear in and out, and no sub-stats are added. If i were to wear 100% diadem gear, all of my sub-stats would be the base amounts.

Thanks.