@Octogon:
Of course Zoro and such can break stone by stepping on it. easily.
Then why hasn't he?
That's a as baseless a claim as saying that Robin is powerless against Sanji and Zoro.
Zoro is a swordsman, and Sanji is a kicking martial artist. Don't assume that they have all these fantastic skills outside of their abilites. One Piece isn't as much "strength vs. stength" as it is fighting style vs style. Zoro might very well be weaker then Yama in a hand to hand fight, but it matter not since he could probably own him with swordsmanship. .
Just as Croc was probably a wimp is physical strength compared to Arlong, yet it didn't matter since his logia was so godly powerful.
This isn't Dragonball, and people don't just "overpower" moves unless it's a skill of theirs. If you want to argue that Robin can't beat Sanji and Zoro, try some other way besides "they'd be too strong for all their moves!" No, I think that Zoro and Sanji would try to get out of Robins sight and attack instead, but they've never just "no selled" attacks.
Hell, Sanji doesn't even take hits that well, he's always gasping and looking shocked and otherwise overselling it when someone hits him. He just has great stamina. Why should he suddenly be invincible against Robin's holds? Can I assume that he can kick Croc's as now just cause I like him more?
The point is, I could except Robin losing to Sanji and Zoro just fine, but damn, can't you think of a more creative way that doesn't make Robin so pathetic? Robin is at the very least a worthy opponent for these two. Don't act like Zoro and Sanji are so invincible, they are strong men with flaws, otherwise they wouldn't have trouble with people like Wanze. Don't forget that the people who Robin has lost to defeated Zoro and Sanji almost as easily.