1. It is POSSIBLE (not very probable but still possible) that someone, somewhere, somehow would have written the exact same book. And since it's possible[i] it is included. And again we are talking about possibilities here not what actually happens. So if JK was killed, it still would have been [i]POSSIBLE that if she weren't she would have created HP and and a billion other things as well.You don't seem to get the implication of the word "possible". That one word is what makes it infinite. You ever hear the phrase "The possibilities are endless"? That's the case here. One single person has the ability to imagine an infinite number of ideas and write them down. Just one person.
But it seems like you are off of the idea that we only consider current Earth bound books and that's a good start. 👆
2. Kinda already answered this but at least we can agree that "all books possible" is a much much much higher number than what you originally tried to calculate. Well beyond anything In DB
3. Comics don't always makes sense but even tho Shazam has his power based on Herc, he is actually stronger than him. Maybe it has to do with him being magical in nature but his feats are above Hercules'
4. Yeah........ Superman from Earth 2 had just flown through a Red Sun and lost his powers. He was basically just an older man at that point. That was a very poor example
As for Doomsday.... well Strength is not durability. For instance, Batman has taken hits from a mind controlled Superman. Doesn't mean he can dish out that kind of power. And Hulk has crazy ass strength feats but he gets cut all the time. Doomsday doesn't have to be stronger that Superman to hurt/kill him. So another poor example but a common enough mistake.
Also you forget that Superman has many different writers and stories that need plot and struggle. One writer may see Superman as weaker than another and that's why you have conflicting feats. DC has addressed this with his mental blocks. Sometimes he can push himself further than other times. So to answer your question, the best way to look at it is Superman has infinite strength but doesn't have access to it at all times. That's why we get him needing help to push a moon but benching the Earth without issue for days on end. He basically is as strong as he needs to be. His strength is a plot device.
The writer clearly stated the book had infinite pages. If it didn't, they would have either made that clear or never stated it did in the first place. You trying to debunk it just shows your biased option here. You want Goku to be stronger but he just doesn't have the feats to compare to Superman's 75+ year history and there is nothing wrong with that.
Also I just realized you tried to use Cell's non canon strength feat as evidence for Goku. Even if the feat were admissible, it isn't tho, it's not a Goku feat. You can't feat swap unless you want me to use feats from Superman's "peers" as evidence for him too. That's a can of worms I'd rather not get in to