Both weren't 7's as kids and it shows in their robotic play. This is a complement not a knock on them.
I grew up in Brisbane and played with/against a host of players - Thurston, Smith, Cronk, Clint Amos, Parker and a pair of brothers from Wigan that went back to England to go on and have decent professional careers (Mark and Martin Gleeson).
Cronk played 7 in juniors for souths acacia ridge in Brisbane. He played flyhalf (10) in rugby and for the RU Australian schoolboys which is about as close to the halfback role as you can get in that code. The half back (9) role in RU is closer to a dummy half in league imo.
He then went on to play in the centres, at 6 and at 7 for Norths in the Melbourne feeder side in QLD cup He was then coming off the bench for Melbourne in a play anywhere type role because he was too good for QLD cup but stuck behind I think Matt Orford at the time.
To say he never played 7 as a kid is not accurate but I do agree with the sentiment that he was robotic in many ways and there are similarities to Nathan in that he worked extremely hard on perfecting everything in his game and maximising his lack of creativity as a half. Cronk is the epitome of dedication can outperform talent. Nathan has substantially more creativity than Cronk did.