I don't deny that Priority and Rapid Spin are important, however, as I have already stated above, I cannot include priority moves since they are too wide a bracket with too different a range of effects (typings, power, etc etc. Unlike the recovery moves that I bunched together, these things do not all have nearly the exact same effect to include in one slot, and none of them are individually so common AND widespread across tiers to fetch a spot.)
And I do not add Rapid Spin primarily because the second condition is not fulfilled by it: distribution. Unlike Defog, which is available to nearly every flying type and a large range of non-flying types across tiers, Rapid Spin is exclusive to only a small number of users throughout the tiers. It's the same logic as, say, Bullet Punch. No doubt that BP is the reason why Scizor has so much usage, just as RS is a key factor behind Starmie's, but simply because a move is greatly abused by one or a few Pokemon (no matter how common that Pokemon, and consequently that move, is in any given tier) it cannot sit in this list, since it is not widespread. Rapid Do N certainly does get an honourable mention, though.
And I think protect is very important, across tiers.