Acupressure is based on luck, like Inconsistent, yes. But there is a major difference. Inconsistent Pokes run Substitute + Protect to stall the foe long enough for the Ability to provide the boosts, whereas Acupressure doesn't kick in by itself; you have to use it, and using it leaves you open to attack (or worse, Taunt). That's what keeps Acupressure from being broken, and that's also why you don't see it in every nook and cranny of the metagame; you hardly see it at all.