That assumption was never made. Rather, it was the speculation on what allows these people to retain said memories to begin with. That speculation resulted in the conclusion that it must be a mixture of both one’s will and one’s love for both Riki and Rin.
I still maintain Kyousuke held the position of “god” for a very good reason. While your interpretation was an interesting aspect I had not thought of, I still do not think it follows through. First and foremost, why wouldn’t they want to make any changes themselves? Your earlier argument of Masato not wanting to change the world:
Masato was never smart to begin with, let’s be fair. He would not have had the mental fortitude in order to maintain the cohesion the world required, let alone being able to alter it at will.
So with that said, what about Kengo? He’s obviously capable of being able to change the world. If that’s the case, why couldn’t he? Especially if you believed that:
Frankly, this doesn’t make sense, at all. There was no indication in the novel, from what I can recall, where Kengo believes he can still save Riki and Rin in the real world. Nor were there any indications that he did not want anyone else but the original Little Busters cast in there.
If anything, he wanted the dream world to stay around. He felt that Riki and Rin did not need to grow up, but rather, hide in this paradise everyone had created. In reality, Kengo was selfish and wanted to spend the time they were able to make in the world with Riki and Rin forever. The thought of death was emotionally debilitating as it meant he would never be able to see any of his friends ever again.
Also, the notion of:
doesn’t make very much sense either. In what way were the female cast actively (key word here) maintaining the world for Riki and Rin’s sake? While they may have helped create the dream world, they still were more fixated on their own burdens they were unable to resolve in the real world.
Kurugaya’s “burden”, however, was unique in the sense it came up in the dream world. Prior to this, she had never experienced the kind of closeness the cast of Little Busters had to offer. Let alone someone confronting their feelings to her. This inevitably prompted a very strong desire to keep the closeness she had experienced. Thus, the sub-loop.
Now you might ask: “If that’s the case, shouldn’t Kengo also be able to control the world like her?”
The answer to that would still remain: no.
When you continue reading into Kengo’s character, you find that he loves Riki and Rin to an almost childish level. He wants to spend his time with them forever. He knows what he’s doing is wrong but still wishes for that instead. Due to that internal conflict within himself along with the lack of resolve to help Riki and Rin eventually grow stronger, Kengo can not have the same god-like powers Kyousuke possesses.
Even if he may be able to exhibit some sort of control, it will inevitably end similarly to Kurugaya’s. If anyone, Kengo should know after having to see the world repeat over and over again.
In essence, to suggest both Masato and Kengo had “no desire to change the world” is to also suggest they don’t have any resolve either, which is obviously not the case. Let’s look at Kyousuke once more.
What do we know about Kyousuke? Never has it been hinted that Kyousuke is weak in any way. Never has it ever been hinted Kyousuke is incapable of doing anything. Instead, all we know is just how strong willed Kyousuke is. How loving Kyousuke is. How determined Kyousuke is, even if it means going against principles. The only time we ever see Kyousuke’s weak side is when the world is about to finally lose its cohesion, and that is when he finally broke tears. With a person who’s personality seems almost damn near unbreakable, someone who brought together the Little Busters himself, who better to be the god of the world than Kyousuke?