In a deck running 20 pokemon, you're going to find ~4 pokemon on average with palossand's GX attack.
And that's assuming your opponent's deck maintains a relatively normal distribution of pokemon throughout the game, which it won't, because people search out pokemon cards more often than trainer cards, reducing their density in your deck throughout the game.
Sometimes you'll hit 7 or 8 pokemon, one-shot something, and discard all of their GX's, but those situations are rare, especially considering palossand's setup time which gives your opponent the chance to get those pokemon out of their deck.
It's a cool attack, but it's an attack for the players looking for meme attacks, not a competitive choice.