The Evans vs other PG's is way over played. As people point out, their PG's arent the ones guarding him now if they arent a good defender. And if you want someone else on Evans just set a screen or 2.
Kevin Martin is a full size SG and a shooter. He has abused PG's that try to guard him. People think that didnt work so why would Turner be any different? They weren't exceptionally better. And your taking about adding a rookie not a vet.
Teams have problems stopping CP3, Parker, DWill so why would Wall be any different?
Oh, and Wall is a decent defender too.
You aren't seriously trying to compare Martin to Turner are you?
Turner's ball-handling skills are as good as, if not better than Tyrekes. I remember a poll regarding Martin asking what area of his game needed the most improvement. Since defense wasn't on the list, ball-handling was the overwhelming answer, and I agree completely.
Next, Turner showed the ability to post up his man. Kevin couldn't post up his man if his life depended on it, that's just now how his game is constructed.
So if you pair Tyreke and Turner together in the back-court you have the following situation:
1.) Tyreke is guarded by the other team's PG. Tyreke is going to take advantage of that all day by either muscling up and driving to the lane, or posting up that guard.
2.) Turner is guarded by the other team's PG. Turner will also be able to take advantage of that all day. Most likely by using his height and length to either shoot over the guard or to post him up. Turner will also be able to have a live dribble and dribble-penetrate and stop for the mid-range jumpshot or take it to the rim far easier than Martin ever could.
Either way, the only way a team would have any sort of success trying to guard that back-court would be to take their own PG off the floor and throw in two defense SGs, and of course, that is to our advantage as well.
Simply put there isn't another PG in the league where teams start the game putting their best wing (either SG or SF) defender on the opposing team's PG because they don't have any PG who has a hope of stopping him.
So the best thing this team could do, would to bring in another player into the backcourt who will abuse the team's PG if the opposing team decides not put their PG on Tyreke. There isn't anyone in the draft better suited to this than Turner, and I would be hard pressed to find too many people currently playing in the NBA who would fit next to Tyreke better than Turner.
Now to your other points:
I agree with you completely in that teams are going to have a very hard time stopping Wall. He's going to be a fantastic player.
But if Wall played against Tyreke and the opposing team put Wall to defend Tyreke, my guess is that the other team would be forced to make changes defensively (pack the interior, big man shadowing, double teams, putting a bigger man on Tyreke, ect.) to stop Tyreke before the Kings would have to make defensive adjustments.
I also agree that Wall is a good defender now, and if he puts in the effort, can be a very good defender at the PG spot.