Fitzpatrick believes the Irish have adopted a similar style of play to New Zealand and has also noticed England benefitting from the southern hemisphere teachings of former Wallabies coach Eddie Jones.
As a result, the gulf in class between the All Blacks and the two Northern heavyweights was fast closing.
"England have really gone to another level, Ireland have real depth and to win World Cups, you need depth, and Ireland's got that without question and so have England," he said.
"I just think that England and especially Ireland have got our number in terms of the way we play the game. They play the game similar to us."
However, the inaugural 1987 World Cup winner expects improved depth around the globe would ensure a more competitive tournament.
England made a statement in beating Ireland in Dublin this year, while Fitzpatrick expects some old foes will also rise to the challenge come World Cup time.
"You throw those two in there along with Wales, who are on the most unbelievable winning streak at the moment, and then you've got South Africa and you can never write Australia off. It's going to be hugely, hugely competitive," he said.
However, Fitzpatrick was not so optimistic about France's prospects and suggested they might need to follow the lead of Wales, Ireland and England and appoint a foreign coach to help them return as a world force.
"If the All Blacks feel they have not got the best New Zealand-born coach in the world they will look outside," he said.
"Whoever would have thought England would call on an Australian to coach their national side, but they made a bold call and went for the best they could find.
"I know France have said it is something they will never do but they need to do the same (as England and others).
"I do not know (Jacques) Brunel and I am not having a go at him but something is wrong."
While confident of the All Blacks chances of a three-peat, Fitzpatrick believes the staging of this year's tournament at a "neutral venue" would ensure northern and southern hemisphere teams enter the World Cup on a level playing field.
"No disrespect to Japan because they can beat the big boys as we saw in 2015 [when they defeated South Africa] but it's the first neutral World Cup in terms of the home advantage."