Johns was a better player than Thurston. Johns dominated at all levels, especially at club level where if he was fully fit throughout the season it seemed like he was twice as good as anyone else.
With Johns Newcastle were a premiership contender, without him they were a wooden spoon contender. Thurston was the dominant force at the Cowboys, but as we have seen without him in the side they were still a premiership contender, and with him in the side they could still battle for the spoon. It was more the coming of Morgan, Granville, Taumalolo etc that put the Cowboys on track for the 2015 GF, rather than Thurston on his own.
At state level we've seen Johns come in and make us wonder how QLD even got close to NSW. We lost Johns and didn't win for another 9 years. Thurston came into the QLD around the beginning of the streak, but that also coincided with the coming of other stars Smith, Slater etc and Joey's retirement.