So, in short, "power creep" is simply a way of saying that with many new generations the Pokemon get stronger, so threats from earlier meta games can seem less powerful in the current meta game, and there are new things to watch out for. In relation to Scizor, it could stay in OU, simply because the tier in general would get more powerful. Lucario is also a good one for Fairy-killing, although it lacks Scizor's resistance to them, and Venusaur and Gengar are potentially other good choices against Fairies. Many of the dragons might also drop a tier (possibly) because they might be completely walled if the opponent sent out an Igglybuff (OK, maybe not an Igglybuff, but you get my point).