Would the Warriors make this trade?
Golden State are giving up a lot in this deal -- Wiggins was an All-Star less than two years ago, Kuminga and Moody are third-year lottery picks (with the latter having made a huge impression in recent games), Payton is an elite perimeter defender who's value to the franchise continues to be underrated, plus a future pick that will convey when Stephen Curry is 40.
This is an overpay, even if the Warriors were to re-sign Siakam in free agency. If he were to leave in the offseason without compensation, it would be a genuine disaster. That alone would be enough for the Warriors to say no, regardless of the assurances Siakam and his management may try and give.
Golden State would have to be supremely confident that Wiggins won't return to his All-Star form, and therefore be certain that Siakam is a major upgrade. You could argue that Wiggins is a much better fit -- he's a better three-point shooter and without him and Payton the Warriors would have nothing in the way of perimeter defense.
It may have taken a while, but Moody is starting to show signs of being a long-term starting caliber player? The Warriors would be hesitant to give him up now, and so too Kuminga who they've invested so much in. In fairness, they do retain a part of their future by holding onto Brandin Podziemski and Trayce Jackson-Davis, both of who have impressed in their rookie season.
Hartenstein is an incredibly good backup center -- one of, if not the best in the league. But with Draymond Green, Kevon Looney, Dario Saric and Jackson-Davis developing, how many minutes does he actually get? Very few come playoff time when Steve Kerr will prioritize the shooting of Saric and small-ball minutes with Green at the five.
This is the kind of package the Warriors should be giving up for a genuine star with multiple years left on their contract. Siakam probably doesn't fit the caliber of star the'd ideally be after, nor does he fit the second criteria. Pass.