Both. Let's not dismiss the motivation and even brilliance having fun can produce.
It's already in elite sports.
Coaches are sending teams out with the instruction 'Have fun'. It makes sense and it's a useful approach for anyone who leads a team.
Here's the traditional way. Years ago, I was a television reporter on the sideline of a provincial rugby game. It was half-time and I could clearly hear a coach haranging his players about their mistakes in the first half. How motivational would that be? Those players may have avoided the same mistakes, but their motivation would be to keep the coach off their backs, not the risk-taking and opportunism that leads to brilliant performances.
The 'have fun' approach only seems soft.
Most people want to improve. They are already determined. The need to be competent is one of three 'universal motivators'. Universal, because the motivators work regardless of culture.
Having fun in sports or challenging assignments comes with benefits that tap into that self-motivation. Allowing ourselves and others to have fun allows us to relax while focused on achieving more - being more creative, taking reasonable risks, staying motivated when things don't go as planned.
Fun, and everything that goes with it, beats top-down demands for performance.