Rocky was almost useless when he joined the pro ranks. He wasn't very hard to defeat in amateurs. He had horrible balance. Goldman formed him into the force he became. Tua, while certainly not a finished work, was much more refined when he arrived. I am basing this on the reading I have done on Marciano and firsthand accounts from folks who were in the Tua camps.
Useless, but strong enough to blow out other novices that traded with him using raw power. Tua had no size advantage here, you think he is outpointing the Rock behind a crisp jab?
This thread is regarding a pro match up, not an amateur contest with head gear. I can see lots of possible twists and turns being made to justify the Tua pick.
Charlie Goldman's assessment of Marciano at this stage versus Lou Duva's assessment of Tua should be enough reason.