1. Tashigi defeated Monet
2. I'm aware it's my opinion. But I am not wrong. Sure, Zoro is more badass than those people. But why is that that's all you have going for you?
Law, Ace, and Doflamingo all of have better backstories. Their personalities are better written, ties in with their personal stories better than Zoro's, and have better motivation to do what they're doing.
Crocodile, Doflamingo, Akainu and Rob Lucci, when analyzed, are good literary symbols of different things. Zoro is a literary symbol for nothing whatsoever. There is no deeper meaning to his character, you don't look at Zoro and see some kind of reflection on the world like you do with these four villains. Aokiji is also the same, and Kizaru if you look hard enough.
Zoro is badass yes, but that's what his character revolves around. He's the generic, antisocial tough guy found a dime a dozen. The fact that Zoro is the definition of badass is why he's such a weakly written character, he has nothing else truly going for him. "Getting lost and doing badass stuff, while kinda mentally slow." That's it, you just summed up Zoro's character for any non-OP reader.