It does. In swordfighting, or any kind of fighting really, a more experienced and knowledgeable fighter will usually win regardless of potential physical disadvantage, simply because he will have greater knowledge of possible actions/moves, better judgment of when to use which move, better ability to predict how his opponent will react and better ability to adapt to the changing situation.
To get a better idea of what I'm saying, try fighting Dante at Human, and then try fighting him at Human at New Game Plus, where he will have more abilities avaliable. After that, try to fight him at Devil Hunter or Son of Sparda mode, where he will not only have those abilities but will be faster and use them better. Then compare all three. I know it doesn't really compare to the reality, but it should give you an idea (and in reality, you don't have half-demons running around, so...).
See above. And "so many ways" is quite a large number of ways.
There are quite a few types of love, you could say that Dante has love for humanity in general.
He can, but it won't be easy.
