I don't like comparing guys to Russell Westbrook, who is approximately the most athletic person of all time. Payton II is an impressive athlete in his own right, but he isn't going to physically dominate the NBA the way RWB does. And obviously, there's the massive age gap which has been mentioned.
This is why I posted the pre-draft measurements that were available for both to show that NO Westbrook is not more athletic than Payton II. They're physically as identical as two players can be.
If you're interested please watch these:
Beating Oregon down the floor and finishing in transition
https://youtu.be/fVYPJlnnoJwHalfcourt offense, screen into drive and dunk over two players on Kansas
https://youtu.be/72m7YlZJ1PMSecond dunk on this clip, secures rebound, one dribble, two steps dunks in traffic
https://youtu.be/tBeqKSxHxjUThere's a lot of misconceptions about Gary Payton the II out there and people are sort of refusing to actually look into him, mostly I think because as you cite "he's older." But in my mind, if you can get Russell Westbrook 2.0 (or even 70% of that) at any age you'd do it. If for no other reason than to have an athletic defensive guard who can physically match up with the other uber-athletes of the NBA for a few minutes a game.
He got Oregon State into the NCAA tournament after a 26 year absence. He lead the team in scoring, rebounding, assists, and steals. He also set the single game school record for blocked shots (7). He essentially was the whole team. He'll be the same age Draymond Green was as a Rookie - and just like Draymond he's projected to slide into the second round... I get that a 23 year old Rookie may not have as much "potential upside" as a 19 year old, but three NBA seasons from now when he's 26 is and a walking triple double is anyone going to care how old he was as a rookie?
Finally please ask yourself how's a guy who has the same height, size, wingspan, and athleticism as Russell Westbrook, who was a four category monster, and the leader of his college team, who's seen the NBA lifestyle up close before college NOT going to find some level of success in the NBA?