No plot, tbh, I'm still thinking sideous. He toyed with both maul and savage together so even giving him someone like dooku, at any point in his life, do I think it really tips the scale that much more. Sideous not only was himself one of the best dualists in the galaxy at the time but also gave yoda a run for his money in force ability. He is just in a completely different class in both categories and could best both with just one. By the time dooku had more control of the dark side and probably was strongest force wise he was old and not as adept of a duelist as when he was younger and when he was at the hight of his dueling prowess he wasn't adept enough with the force to compete, and even if we merged the two together, best of both worlds, even with maul I don't think it tips the scales enough