RealGM

Who do you think would peak higher in today's league? Assume both stay healthy.

Honestly think this depends on how you think Duncan's traditional big man game transitions to the modern era. Peak Duncan was certainly mobile enough to provide great post protection and solid offensive production. Doubt he would (even with modern coaching) have extended his range all the way out to the 3, but his inside game and middies would definitely a valued skillset. He's also the quintessential system player, which I think is key to being valuable in today's x and o driven game, without being an amazingly intuitive passer.

Kawhi (even in his dotage) remains the model of a modern wing offensively and remains able to create his own offence in a variety of ways with terrific efficiency. At his peak, think you can reasonably argue that he surpassed Duncan's production (impact is a separate question). Defensively a smothering black hole of annoyance, especially valuable in an era of perimeter-led offenses. Leonard's offensive and defensive peaks remain distinctly separated by some years, which (compared to Duncan 2003) arguably marks him down.

Peronally, think I still take Duncan, although his relative value at peak is arguably a bit lower than it was in his time, but both are (injury/load-management/fictitious shell companis aside) great franchise centrepieces.