There are a lot of arguments here that could be dismissed if you ask yourself, "How does that happen when we look at an equivalent situation in strength?"
For example - How do we determine what a 6 to 8 intelligence character can think up? We make a judgment call and assign a difficulty to it, usually based upon a DC.
Let's say I put a really big rock in my campaign world. A PC walks up to it and says they want to lift it. At this point in time, I do not have a measured weight for the rock, or any real idea if it is awkwardly shaped so as to make it more difficult to lift than other rocks of the same weight. So, as a DM, I have to decide how to handle it. I determine, in my mind, exactly how big it is and decide whether the PC can just lift it because they have a high enough strength that it likely is under their lifting limit as stated in the book - or I decide it is big enough that I'll require a strength/athletics roll. If I decide on a roll, I have to set a DC.
Let's say I put a puzzle into my campaign world in a carnival booth. A PC says they want to solve it. At this point, I do not have the puzzle worked out in fine detail, and no real specific idea how it is to work. So, as a DM, I have to decide how to handle it. I determine, in my mind, exactly how difficult it is to solve and decide whether the PC has a high enough intelligence to just solve it (based upon their passive intelligence), or if they need to make a roll. If I decide on a roll, I set a DC.