Meta-defining primarily means that it's the deck that either people play, or people play a deck that is intended to beat. It's hard to say if it is that at this point, but it certainly seems the case - we'll see after Oceania, though. Whether it becomes dominant over the long term or not depends on whether it is possible to play a deck that both consistently beats PZ _and_ can beat other decks reasonably frequently. Think Celebi-Venusaur; that deck handles P&Z handily, but it's unclear that it can beat other decks as consistently for it to be played sufficiently itself.
That said, I think you're selling it short. It's not super-consistent, true, but if it works it wins most matchups - even C&V has a hard time against it when it sets up turn 2. Many one-prize decks are quite beatable with it, as it takes them too long to be able to deal 240 damage; it takes prizes consistently on turns 2, 3, 3, 4, 5, 6, and many one prize decks just can't beat two P&Zs that quickly (not to mention that it can turn to Tapu Koko or Zeraora to take some of those, requiring the opposing deck to beat three GXs to win without repeated guzmas).
We'll see if that inconsistency ultimately is a problem, or not. I don't have a solid sense of whether it's going to be or not, nor really does anyone else I suspect - it takes having 300-400 people in a room together play it out, with 50-100 of them playing P&Z and hundreds of others playing other successful decks and counters, to really find out.