Running away and delaying the inevitable doesnt add to difficulty of the fight, maybe if it ever worked out in picas favor by landing a hit like in usopp vs that fish guy in arlong arc, but it never did work that way for pica.... but i do agree with the rest.
Zoro wins no doubt about it. The difficulty depends on how long they can prolong it but you can guarantee he is not gonna fall to these 3.
You're lying to yourself if you see these 3 being able to actually put Zoro down.
The only reason Zoro won against Pica was because he was in statue form. He narrowed the space down Pica could be in and forced him out.
When it's 3 against 1 Pica will never be in his statue because that thing is useless to fight against 1 person. He will be in the ground the entire time.
Zoro has shown that he wasn't able to counter that, he could only block and dodge until Pica decided to come out.
So pica being in the ground absolutely adds difficulty, because while he fires charlestone for Zoro to cut, he also is balancing on a flag like surface and dodging Trebol's sticky stuff that is fast enough to hit a fairy.
Zoro (and Luffy too) is an idiot when it comes to fighting ability users, it always takes him a long time to figure out what is going on and he doesn't beat it by being smart, he always beats it by relying on strength. But there is no way that he can deal with three tricky abilities at the same time. It is a matter of time before Trebol hits him and then it is all over.
Even Law and Luffy had difficulty with hurting Trebol, so it's stupid to think that Zoro comes in and clears it 3 vs 1.