Italy, who suffered 10 defeats and won only once – against Samoa – in a disastrous 2014, are expected to be given a wake-up call by defending champions Ireland in their Six Nations opener at the Stadio Olimpico on Saturday.
Brunel has already labelled the Irish the "strongest side in the northern hemisphere" and believes their club success in the Celtic League is key.
"The Irish are very strong, and they're confident. Their players are used to winning in the Celtic League, whereas the Italian franchises are only used to losing," Brunel told AFP.
Italy head into the competition looking to make amends for finishing with the wooden spoon last year, the first time the Azzurri finished last in the Six Nations since 2011.
They made part amends for their forgettable 2014 campaign with more promising displays in a 24-13 win over Samoa, a narrow 20-18 defeat to Argentina and a heavier reverse to South Africa (22-6) in November.
But the Frenchman said Italy – partly because of a smaller pool of quality players to pick from – are still struggling to produce the kind of performances that would allow them to hold on to narrow leads as well as fight their way back into match-winning contention when trailing.
"It's true that 2014 was difficult, mainly because of our lack of efficiency," added Brunel.
"Over the past two years we suffered two last-minute defeats to Scotland, two narrow defeats to Argentina, pushed England to the brink at Twickenham, and in June suffered defeat to Japan and Fiji in matches we should have won.
"We had the chance to beat Argentina, against South Africa we were trailing only 15-6 at half-time and on a par with the second best team in the world.
"That makes about six or seven games we lost out on through our lack of efficiency. The results are there, but there is a very thin line between the 2014 we had and what it could have been.
"Our performances in November gave us a bit more reassurance, even though the results weren't good."
In 2013 Italy showed real signs of progress with the Azzurri beating both Ireland (22-15) and France (23-18) in the Six Nations, finishing fourth.
Although Brunel is hoping for a return to those levels, he admits Italy have a fundamental problem compared to the other five countries.
"We know we don't have the same tradition, the same kind of internal competition, the same foundations… and that doesn't give you a great start.
"In our squad the competition for the fly-half position is among (Tommaso) Allan, (Kelly) Haimona and (Luciano) Orquera. In France it's between (Jules)
Plisson, (Francois) Trinh-Duc, (Remi) Tales, (Camille) Lopez, (Frederic) Michalak, (Lionel) Beauxis… it's not the same!"
Brunel also said Italy have "lost the balance" they once had between their attack and defence: "It's a mental problem, if we attack we think less of our defence. Yet, defence is the best means of attack."
Without injured South African born lock Quintin Geldenhuys, who is out of the campaign with knee ligament damage, Brunel fears their pack is "not as strong".
"He was like the pulse of our pack because he gave us consistency," he added.
With Ireland, as well as France, in Italy's World Cup group later this year, the Frenchman admits Saturday's game will be key.
"These games will give us important reference points and the team who wins these game will emerge a little more confident," said Brunel, who nonetheless is hoping Italy make the most of their three home games this tournament.
"It's a year in which we have three home games, so we owe it to ourselves to win at home. I'm convinced we're not that far off the other big nations.
"But for us to win, we need 100 percent precision and 100 percent efficiency. We can't afford to be at 70 of 80 percent."