Kimimaro was far from complete. He couldn’t even find completeness as Orochimarus manipulates and used piper. As soon as he found out Orochimaru found a new vessel he was devistated and had to continue compensating for his self perceived indaquecy the best way he knew how, continue serving Orochimaru and kill whoever he told him to.
Kimimaro found a sense of purpose and a meaning to his life by serving Orochimaru and thus felt complete in his life. This feeling started to shatter the moment his body fell ill and he could no longer serve Orochimaru. Which is why he willingly gets up to fight regardless of the risks to his life. Because to him, nothing is more important than serving Orochimaru and that was his meaning in life. He found his meaning and thus became "complete". This is a traditional trope in writing that humans in real life very much share.
We, as humans tend to feel "complete" or "at peace" when we know what to do, how to do it and capable of doing it. Kimimaro always knew what he wanted to do and how he could do it, though when his body fell ill he lost the capability to do it. That is why in the end he was considered "happy" because he was again capable of doing what he wanted and knew how to do, serving Orochimaru to his dying breath. The only time he wasn't "complete" in this sense was from when he fell ill to the point he got out of the bed to fetch Sasuke.
Life is a journey, most adults aren’t even complete. To be complete means the end. If by complete you mean he accepted being Orochimarus pawn and nothing more then I can see it.
That was the point of Kimimaro's character. The logic you're using is "because only 1 is, no one can be". Yes it is rare for an adult to be "complete" and even more so for a kid to be, but its by no means impossible. Same way that people never find purpose or peace in their lives, some find it early. Same way someone never grows up, some have grown beyond their years at a young age. People are different and that was (likely) the intent with Kimimaro's character. To be "complete" or "at peace" doesn't mean the end specifically, it means that you are happy with what you've done, what you are doing and what you want to do. To do that you must first know what, then how and then be capable of doing those things.
Not to mention that Kimimaro was at "the end" in his life and was content with the life he had lived, he even become vocally mad when confronted with the idea that he was just manipulated. Stating that was never the case, that he always did what he truly wanted, what he felt he needed to and what he was capable of doing, even to his dying breath.
“YOURE WRONG” lol. That doesn’t sound like completeness to me it sounds like some lost kid who’s total life was a lie, someone who convinced himself that he wasn’t just being used and thrown away, which is exactly what Orochimaru did.
As I mentioned above, when Gaara comments that Kimimaro was nothing but a pawn to Orochimaru he doesn't scream in a fit "NO YOU" like you imply. He first comments that he doesn't really care what Orochimaru views him as, he is content with that. He also remarks that Gaara is indeed wrong, as being used implies that you aren't aware and that you aren't doing what you want, that you don't have a personality. Kimimaro is quick to note that he does have a personality, he is doing what he want and he is content with that. The specific dialogue is Gaara referring to Kimimaro as "brainswashed" for saying that Orochimaru will always "remember me in his heart".
Yet Kimimaro also admits that he is nothing but a tool, a pawn, a "arm" of Orochimaru. He is clearly aware of the relationship they have and yet he is content with that. Another important thing to take away from this is that regardless of whenever he thinks Orochimaru cares is irrelevant in this scenario. He is still doing what he wants, what he can and what he is capable of.
And Sasuke being everything wrong with humanity?
I said that he was that in context of Kishimoto's writing, as outlined by Obito and Madara. Those that love will learn to hate, that is the flaw of mankind as they see it. They aren't inaccurate either and Naruto admits this, but refuses to believe that is all there is to it. In other words, even if it is futile, Naruto believes that its worth trying to prove it wrong.
Sasuke was all about justice. He went on a journey to avenge his clan and still refused to kill innocent people and was even chose to kill Orochimaru instead of giving him his body seeing as how Orochimaru was causing more harm to people than his brother ever did.
Sasuke embodies the concepts of "learning" and "evolution" which is clearly demonstrated in his dialogue. He also didn't kill Orochimaru out of any other reason than spite and power. He states to Naruto that he doesn't care if Orochimaru takes his body or not as long as Itachi dies. To ensure the strongest survive he attacked Orochimaru and had a battle. Regardless of who wins, the stronger will survive and that person will face Itachi. He survived and therefore was the strongest in mind and body. Sasuke also only ever refused to kill innocents until the point where he lost faith in the world, when his hatred couldn't be focused on one person alone.
Sasuke's main flaw through the story that he realizes himself after meeting Itachi again was his limited knowledge. He lashed out in anger based on nothing but ignorance, he didn't know anything and just acted on pure emotion. We as readers see this as childish and stupid, but in reality this is what a lot of people do as well. He wasn't focused on solving the bigger issue, but the one right in-front of him that believed was the larger issue.
Sasuke lives to erase evil.
Sasuke is neither evil, nor good. He is a gray area as opposed to Madara and Naruto. He is suppose to be that, he is suppose to be the middle ground. He acts as this through his actions of choosing the path of neither wholly good or wholly evil and this finally accumulates in what he sees as "The Way of Shinobi" at the end of the story. "A person who endures so that others don't have to." Combining the morals of Madara and Naruto, someone who takes it on to themselves to protect those who can't like Madara did, but one who does it for others and not for oneself like Naruto wish was born from.