Nash's jumping ship with Hall definitely played a big part in WCW's rise and subsequent boom period which made them the closest company in the world to WWE by a wide margin; but by comparison Nakamura's transition to his current look and personality, along with the rise of Tanahashi, were what revived New Japan from a down period and sparked their latest boom period and rise which has made them the closest company in the world to WWE by a wide margin.
Nash had a lot of championship success(mostly due to backstage pull), but never had a strong and profitable reign as champion. Nakamura on the other hand also has had a lot of title success- three times holding the IWGP heavyweight championship, while also becoming the face of New Japan's IC title, winning it five times, having the longest ever reign, and single handedly raising the profile of that championship to near equal footing with the IWGP belt where it now sits just behind that belt as the biggest title prize in the pro wrestling world not competed for under the WWE's umbrella.
Also while Nash performed well(in a win/loss sense never in a quality matches sense) with absolutely everything possibly imaginable stacked in his favor; Nak has been able to perform thousands of miles beyond expectations, even after traveling thousands of miles to continue his career in a different hemisphere.
Nak has already entered the WWE world, owned NXT, went months undefeated, won the brand's world title twice, defeated many of the top guys that brand has produced, and that's just the start as he hasn't even gotten a chance for his main roster push yet. He is already the most successful Japanese star that the company has ever pushed.
Nash has a lot to hang his hat on, but he should. With his size and the behind the scenes pull he built up, he would've had to have been the worst wrestler ever to have not achieved at least as much as he did. Nakamura on the other hand achieved an arguable amount of success on a relative scale, and did it all on the back of his own magnetism, personality, charisma, originality, and enigmatic appeal. I would have voted Nakamura here based on his career in Japan, even without accounting for the success and groundbreaking, game changing, door busting in for perception changing and potential future of the business altering effect that his jump to WWE has yieded. Throw that effect in and the fact that Nakamura lost nothing from his star or his momentum and only upped his status by taking the McMahon money, and he locks this match-up up for me.
