As I see it, Kyousuke is the perfect leader figure for the kind of group the Little Busters are. Turning it around, you can also say that the Little Busters became what they are thanks to Kyousuke.
He is an indispensable character for this VN and no one else could’ve taken his place.
Kyousuke’s burden was a heavy one and the task he had tackled was enormous. He had to turn the weak, extremely dependent Riki and Rin into people who could face the cruel fate of losing all their friends and classmates, as well as standing on their own two feet and live a normal life after that.
Before Rin2, his methods were flawless. Every new task was FUN at the beginning. He found new friends for Rin and had Riki recruit them. In exchange for having them participate in his plan, he had Riki help them deal with their regrets and face hardships. He sent letters to Rin to have her improve her social skills (and common sense). Loop by loop, Riki and Rin were slowly maturing and growing stronger.
Up to there, his methods were very fitting for those two.
But Kyousuke is not perfect. He’s just as human as anyone else. He has his own flaws and he makes mistakes. Since he held great power and responsibility, his mistakes resulted in causing a lot of damage. He grew overconfident and rushed things. With his goal in sight, he became cruel and put everything on the line. stopped being choosy about his methods. He destroyed the Little Busters in order to proceed with his plan, making Riki and Kengo his enemies. But he still failed and ended up breaking Rin, who wasn’t up to the task he forced on her just yet.
However, Rin2 was not a complete failure. After all, Riki had sworn to become stronger. His growth was almost complete.
Left alone with his guilt, Kyousuke still refused to give up. He left the details up to Riki, only occasionally stirring things up or giving him a hint and focused on taking care of the gas leak.
Finally, Riki had succeeded in taking Kyousuke’s place and he didn’t stop there. He exceeded all expectations and together with Rin, brought about the perfect ending.
To me, Kyousuke is one of the best-written characters. He has amazing qualities, but he’s not perfect. He is a believable and relatable character.
Every group of friends should have a Kyousuke ^^
Let’s not forget that, even as a kid, Kyousuke was already a savior. He saved Rin, Masato, Kengo and Riki and made it possible for them to play like normal kids. He essentially gave them a proper childhood full of fun and happiness.