Thats not true yoda fights in a way that outclasses and tires his opponent like hell but never aims to kill quick. He would tke longer than need onone and might run out by he second oponent. Maul is also underestimated and if he had survived would have been close to dooku(he was able to easily defeat qui gonn). Vader is also underestimated as people just think of the vader in the original trilogy and get put off. What i think of Vader once he is put into his suit is that he gains a lot more strength. He gains a lot more strength in the force and he becomes way more disciplined in lightsaber combat and more precise. The only skill of his that i think got worse was his speed. The fact that he was the chosen one also shows that Lucas wanted people to know he was extremely strong (as the chosen one in any film is usually one of the strongest such as neo in matrix)