Not using Tapu Koko isn't a bad thing. Tapu Koko is not an every game card, but it's there as free retreat, forcing the 7 prize game, and as a source of filler damage if you don't want to commit your Zoroark GX to the active (i.e. your opponent has a Ho-Oh GX with 4 energy on it and you don't want to get OHKO'd by a choice band attach next turn). And of course, Tapu Koko is just amazing in any deck that wants to Guzma. Perhaps it would be wiser to cut Tapu Koko to 1 to have 3 float stone so that your Decidueye GX can rotate more often, but I don't think that change is necessary. The 2 Koko seems more important to me, especially since you are interested in max bench space. Tapu Koko is never a waste of a bench spot if you need free retreating or a Guzma pivot. Since most people are going to be stacking their benches full for their own Zoroark GX, you can probably expect Tapu Koko do be committing the full 120 damage to your opponent's side of the field (20 per Poke), and then if you feather arrow 3 times you've still done mathematically 180 damage during that turn. Once I get my Zoroark GX's online I'll be testing this deck to see if Koko is needed or not. My hunch is that there's nothing better to play in place of it at the moment.