Sir Graham Henry says the All Blacks-Lions series should have been decided by extra time, describing the draw as an anti-climax.
And he also suggested that constant success may have lulled Steve Hansen's squad into believing they were better than they actually are.
Writing in the Telegraph, the 2011 World Cup winning coach weighed in on the controversial ending to the third test at Eden Park, criticising the laws after referee Romain Poite reversed his original decision against the Lions.
And he said it was now clear that the greatest challenge to All Black supremacy was coming from the northern hemisphere, with Australia and South Africa fading.
Sir Graham reckoned: "As for the incident over the penalty for offside that became a scrum for accidental offside, the law is an ass. The penalty was given and that should have been it. As it was, the scores finished level and I would have liked to see extra-time being played.
"A draw after such a magnificent contest was an anti-climax - unlike the tour itself which has been a joyous experience for everyone here in New Zealand. We have all loved it. The next tour in 12 years' time cannot come quickly enough."
He said there had been terrific lessons for the All Blacks, as they build up to their defence of the World Cup in Japan in two years time.
"The greatest challenge to the All Blacks as world champions is currently coming from the northern hemisphere," he wrote.
"The southern hemisphere has gone backwards while the Lions have shown just what is on offer in the home unions. The 2017 Six Nations was the best there has been for a number of years and now we have seen the challenge that the Lions have laid down for the All Blacks.
"Over the next couple of years the signs are that the All Blacks will face more competition from the northern hemisphere countries than they will experience here in the Rugby Championship. Australia and South Africa in particular have tailed off and that is a bit of a negative for the All Blacks.
"It is not that the All Blacks were complacent as to what was headed their way on this trip but it is a pretty young group and when you have won so often in recent times it is very hard not to think that you are better than you actually are, to believe that you are a little bit infallible.
"The All Blacks do not get beaten very often and it will be good for this group to experience at first hand the need to find solutions within games to what they have been presented with."
He reserved special praise for the Lions' defensive system.
"The All Blacks will also have realised that they need to be true to their natural game which is to be bold and to take the game to the opposition," he said.
"They did not do that in the second test in Wellington although conditions were filthy. However, being expressive is what they are good at, as we saw in the opening 20-25 minutes at Eden Park last weekend," he said.
"They had chances, created openings, good openings, but they did not take them. Some of that was due to the pressure the Lions' defence put them under but it was also poor execution.
"The Lions deserve huge credit for not allowing the All Blacks to play their game. That is what the New Zealand management will be looking at going forward, how to break down the rush defence with its line speed and the umbrella format with the man in the middle pushing up.
"You have to pay tribute to Andy Farrell's defensive system, which has been as good as anything I have come across.
"The same is true of the manner in which Warren Gatland and his coaches have managed to bring this group together in such a short space of time.
"It is an amazing achievement, well beyond the expectations of most people here. The backbone shown by the Lions was quite remarkable."
Henry said Lions coach Gatland's pre-tour prediction that goalkicking would be an issue proved correct.
"There is a wee bit of a question mark over Beauden Barrett's goal-kicking ...if (Owen) Farrell had been kicking for the All Blacks, the series would have been won," he said.