That doesn't prove he is ENTJ. Infact that could very well be INTJ.
Sometimes it is best to go with Jung terms to type a person (I, N, P, J etc) rather than typing him on MBTI terms - Te, Ni, Fe etc.
Focusing on this part of your post - and ignoring the fact that you confused Jungian with MBTI nomenclature - sometimes it is best to look at type descriptions. Either Jungian or MBTI will do.
http://www.personalitypage.com/ENTJ.html
ENTJ - "ENTJs are natural born leaders. They live in a world of possibilities where they see all sorts challenges to be surmounted, and they want to be the ones responsible for surmounting them. They have a drive for leadership, which is well-served by their quickness to grasp complexities, their ability to absorb a large amount of impersonal information, and their quick and decisive judgments. They are "take charge" people. [Palpatine attacking Mace Windu without a moment's hesitation.]
ENTJs are very career-focused, and fit into the corporate world quite naturally. They are constantly scanning their environment for potential problems which they can turn into solutions. They generally see things from a long-range perspective, and are usually successful at identifying plans to turn problems around - especially problems of a corporate nature. ENTJs are usually successful in the business world, because they are so driven to leadership. They're tireless in their efforts on the job, and driven to visualize where an organization is headed. For these reasons, they are natural corporate leaders. [Palpatine visualized the need for a clone army 10 years before actual needing one.]
There is not much room for error in the world of the ENTJ. They dislike to see mistakes repeated, and have no patience with inefficiency." [I don't see Palpatine as having much patience with incompetence and inefficiency, although I imagine you will see it - just because.]
http://www.personalitypage.com/INTJ.html
"INTJs live in the world of ideas and strategic planning. They value intelligence, knowledge, and competence, and typically have high standards in these regards, which they continuously strive to fulfill. To a somewhat lesser extent, they have similar expectations of others. [Palpatine had high expectations of others.]
With Introverted Intuition dominating their personality, INTJs focus their energy on observing the world, and generating ideas and possibilities. [Palpatine was not focused on observing the world, but controlling it.] Their mind constantly gathers information and makes associations about it. [Palpatine shows no indication of drawing associations about the world.] They are tremendously insightful and usually are very quick to understand new ideas. However, their primary interest is not understanding a concept, but rather applying that concept in a useful way. [Palpatine was more interested in applying the ways of the dark force, not studying it like a scientist or bookworm.]
INTJ's tremendous value and need for systems and organization, combined with their natural insightfulness, makes them excellent scientists."
The archetypes of the INTJ vs. ENTJ suggest that palpatine was not the scientist type, but rather the natural-born leader type. ENTJ.
[edit - fixed.]