Nearly everyone aspires towards being a realist, or understanding the situation in its entirety.
What optimism and pessimism are, is how you fill in the gaps of what you do not know - do you fill them in with happy thoughts, or unhappy? Or do you split them 50/50 in an attempt to remain realistic? In which case, you're neither.
I'm neither.
With that said, I find that inspiring optimism is a positive action if you're a leader, even if you yourself are not really optimistic in your thinking. If people have faith in the future (at least faith that if they work on it it will get somewhere) and work towards it in that way, that can only be productive. Pessimism will just make people too lazy to act.
Look at climate change. "Oh, it's too big a problem, we can't do anything about it" - that mindset, even if it were accurate (and in my strong opinion, it is not), is an extremely harmful thing to spread throughout the populace, because it will make people lethargic and unlikely to bother to slow down the problem, much less try to stop it. Even if you don't believe in climate change, reducing pollution massively is something more than one branch of science is saying we have to do, so this should be taken as an opportunity to act anyway, rather than give up.
As for fatalism, I consider the meaning of one's life to default to nothing, unless we work towards a greater purpose and contribute to it with devotion, time and energy. So, I fit in none of the definitions of the OP. Which makes me happy.