Fleming told Radio Sport's Martin Devlin that New Zealand cricket was at an important crossroad.
"We're not really ever going to threaten one or two in the world (in test cricket). We've come close at times but it's only going to be for brief moments," said Fleming, the Melbourne Stars coach.
"We don't have the resources (players). If we lose a few players we're exposed. To compete against the big countries is always going to be a challenge.
"So why not focus on the shorter forms of the game? We can win World Cups - we got close last year. And we can win T20 because we have that type of player.
"Maybe a change of thinking needs to take place to encourage our players to be exposed to these world competitions at the expense of four day cricket.
"There needs to be a change of focus back to the short forms of the game...it is an interesting stage for New Zealand cricket, how everything fits in."
The Big Bash is a runaway success in Australia particularly in drawing crowds to grounds - up to 80,000 have watched matches at the MCG.
The last two seasons suggest the Big Bash - which Fleming rates as the premier competition ahead of the flawed IPL - is here to stay as a major part of the sporting scene. And T20 is having an influence in many ways.
Fleming reckoned that a lot of coaching manuals need to be scrapped, such was the change in batting approaches.
"The modern cricketer like David Warner has taken the aggression from the shorter forms into tests," he said.
"It's about honing the aggression and skills athletes will have then teaching defence, which is a fundamental shift. So many coaching books need to be burnt.
"Past players will be screwing their noses up at what I'm saying. But the norm now is to try to reverse sweep, or go over the top. It is about power rather than timing or finesse."