Broncan, the former coach of Top 14 club Castres, worked under Eddie Jones (64) in preparing the young squad, who lost two of four matches as Australia crashed out in the pool stage for the first time.
"The team's youth did not work at this World Cup, it did not lack experience but collective experience," he told French sports newspaper L'Equipe.
"We saw the players who play in France, Will Skelton (31) and Richie Arnold (33), had a much greater work ethic than the players who are in Australia.
"They are not used to working under pressure, to maintaining precision and concentration. They are used to working at high intensity, that's not the problem, but it's the precision that's lacking. Tactically too, there are very few tacticians."
Broncan, echoing Jones, said the loss of Skelton and prop Taniela Tupou (27) to injuries in one week before the defeat by Fiji had been a hammer blow to the campaign.
"We lost the World Cup the week we lost Tupou and Skelton. Our scrum and pack were much worse without them," he said.
"These two players were not replaced by players of the same quality. If at least one of them had been there, I think we would have beaten Fiji."
The experienced Frenchman thought the training of the pair had been mishandled and that Jones's experiment of bringing in assistant coaches from rugby league and Australian rules had not worked.
Jones, he said, still remained Australia's best chance of putting together a competitive team for 2027, if he was given the sort of backing France coach Fabien Galthie (54) has enjoyed over the last four years.
"There's no time to lose," he said. "The French had four years to build a group. They have been preparing for this World Cup for four years. Australia must take a cue from this."
If that did not happen, Broncan said, Jones might not be around for long.
"Eddie is a competitor," he added. "If he doesn't have the means or if he feels that things will continue as before, it will be hard for him to stay.
"If he senses a real desire from Rugby Australia to create a high-performance environment, I think he will be there."
