Well besides the fact he wrecked him, other than that.. he was too busy running away and doing other stuff, instead of fighting Zoro. When he tried fighting Zoro, he got put down, thats how one-sided the battle was.not much but what damage did Zoro did to Pica before Pica decided to come out of the stone ?
Like I said Zoro has to take initiative and figure the fruit out. Pica can stay in the ground and shoot hist spikes up while Trebol sticks him to the ground with his slime. And his slime is fast and precise enough to hit a running fairy and gear 2 Luffy.
Soooo what is Zoro gonna do when he is stuck on the ground again ?
Comparing a scenario where Zoro had to get Pica, to a scenario where Zoro doesn't need to chase down pica, and can simply sit and counter isn't really a good comparison of scenarios. There is nothing in Pica's arsenal that can be a bother to zoro while fighting the other 2, who he can beat very quick.
Throw his strongest punch? slice slice
Try to sneak attack? slice slice
Nothing Pica can do to beat Zoro.