You might as well be saying, Luke Skywalker wasn’t actually a Jedi, he was just some kid who wanted the glory of killing the Emperor so he tricked Yoda and Kenobi into thinking he cared about becoming a Jedi when really he just wanted to learn some cool skills.
Clear and concise evidence? Yes, let's all be good little automaton droids and believe everything Palpatine says. HE IS THE SITH LORD! Sith Lords are masters of deception. Dooku is not a Sith, he is a rogue Jedi with a noble, aristocratic background, who became tired of the Jedi Council's B.S. If Dooku was a Sith Lord, don't you think he would have killed Yoda? If Dooku was out to kill Palpatine, then I would believe he was a Sith Lord, but Dooku isn't a malicious character. He left Yoda alive out of respect... just like a gentleman would.
The Sith are evil and they are out to kill if things don't go their way. Dooku isn't evil, he's too proud to acknowledge the existence of 'good' or 'evil'. He trained Grievous. Grievous said, "I have been trained in your Jedi arts." How could Grievous say 'Jedi' arts if he were trained by a Sith? I would hardly find this line to be speculative nonsense that I just made up. In fact, it's in ROTS.
Also... why is the name 'Darth Tyranus' mentioned only a couple of times? Why is Dooku intent on keeping his real name instead of being known as a 'Darth'?
Another point to bring up... Luke Skywalker didn't kill the Emperor, Vader did. All Luke wanted to do is succeed where Obi-Wan failed.