England registered just two wins from their six matches at the World Cup, failing to progress from Pool A and lagging well behind their rivals in terms of tactical approach.
The batsmen often played too conservatively in a succession of sub-par scores and the bowlers were easy picking for inventive batting sides like New Zealand, Australia and Sri Lanka.
"You have to be brutally honest and say we were getting it wrong," Buttler told reporters.
"We almost had to play our perfect game to win. It's time to put the World Cup behind us. It was very disappointing but we learned some key messages.
"We have to be looking at scores of 350 and upwards. That's the way the game's going. In a few years we'll look back at the World Cup and say it was a turning-point in 50-over cricket.
"The way (New Zealand's) Brendon McCullum captained, the way (South Africa's) AB De Villiers batted. This was a moment in time when the game changed and we have to follow that lead. We don't have any other choice.
"We have to go out there with that freedom and no fear of failure and play the brand of cricket that is so accustomed to 50-over cricket these days. The talent is there."
New Zealand finished runners-up to Australia at the World Cup, combining destructive, inventive batting with aggressive, economical bowling.
In their Pool A encounter England were bowled out for a measly 123 before New Zealand, led by McCullum's swashbuckling 77 from 25 balls, chased down the target in 12.2 overs.
Buttler believes New Zealand's gung-ho style should be a source of inspiration for England.
"We've seen another side do this, so we can go in exactly the same direction as well," he added.
"It gives the new players a real eye opener as to what international 50-over cricket is now about. We want to win, but whatever happens it'll be a great learning curve."
The first one-day international is at Edbgaston on Tuesday (local time).
