Wall and CP3 have strengths and weaknesses that can be looked at with different viewpoints, but I lean towards Wall from just a pure basketball perspective.
the way he creates shots with aggressive drives to the basket, his court vision, and ability to control the tempo of the game is done better than how CP3 does, in my opinion. The main reason why is because of the fact that he's taller, and better at taking it to the basket, he can take a 7 footer to the basket and take over games with his physicality. He can choose to be a scoring point guard if he decides to flip that switch, because often times he's the best athlete on the floor. He creates opportunities because you truly are worried that he'll flip that switch and decide to put numbers on the board.
I prefer that to CP3's role as a game manager who needs to do a lot of dribbling and probing in order to get things done. He dictates every play of the game, and needs to play a 2 man game more often than not to be effective (pick-and-roll, give and go, etc.). Not to say that Wall doesn't do those things, but he doesn't need to rely on it. Also, it doesn't help that at his height and limited athleticism, he's a streaky shooter (doesn't affect Wall as much because he can just take you to the basket) and has overall hit a physical decline. Not to say CP3's way of doing things doesn't work, but I prefer Wall's style of play.
And by the way, CP3 is NOT a better scorer, Wall doesn't take many shots, but he can take over a game if he chooses to. Wall could be a 23/24 PPG scorer if that was how he decided to play, he's not as good of a shooter as CP3, but CP3's not that great of a shooter either. Wall has the athleticism (which essentially is the #1 reason I prefer Wall) to play the position to it's fullest, I simply don't think CP3 does at this point of his career.
But really, you could take either one you prefer, apples and oranges, I don't think one is overwhelmingly better than the other.
Tl;dr Wall is a better athlete that's why he's better than CP3 in my opinion