Wales also lost twice to New Zealand, though those two games proves the sternest tests the 'Baby Blacks' had on their way to winning the title.
Burnell feels the academies structure is beginning to develop players who feel they can compete with the best in the world at this age.
"It is working on that and not putting some of these teams up on a pedestal. We more than held our own against New Zealand and then we felt just disappointment against Australia because we matched them physically and in terms of pace, but there were just a couple of errors," he said.
"The academies have a major bearing on that now. Players are coming in at 16 years of age and becoming mentally tougher and I do not think we had that mental edge before.
"They are now coming in at 16 and having that service of a true professional and also that bodes well for the future because we are moving forward and that was another major statement in this World Championship."
Wales last achieved a top four finish in the World Championships in Chile in 2001, but the play-off game was particularly disappointing because they took a 21-10 half-time lead against Australia and then had opportunities to go further ahead.
"We got into that lead of 21-10 and just after half-time there was an opportunity when we should have scored a try but didn't," admitted Burnell.
"Then we missed two kicks at goal which was awfully hard on Leigh Halfpenny who finished as the top points scorer in the tournament. Perhaps he would have kicked those two with his eyes shut, but that is no fault of Leigh's because he was definitely one of the finds of the tournament.
"Against the big sides you cannot afford to let them back into the game and unfortunately for us we lost our shape for a 10 minute period and they capitalised and then held on to the end.
"I do not think we were over-awed by playing Australia, there is a disappointment that we did not win and feeling we let ourselves down a bit because of all the hard work which had gone into it.
"People say it is fantastic to finish in the top four but I think we should have finished in the top three."