I'm not sure it always works. Canada has had this system in place for radio and TV for ~50 years. Radio has sort of worked maybe but TV? No way. Maybe once a decade there's a half decent show worth watching.
But not for TV? Is it maybe the fact that music has lower entry requirements for smaller artists to take off ?
While TV requires large scale production, thus if an overworked producer is making a “quota” product for TV, they might actually do what people are describing and rush something just for the 30% time they have to fill in.
It’s interesting because certainly it seems like there’s some relation to scarcity. The time on cinema screens is very scarce so the French cinema example seems to have worked. While radio, even though there are a lot of radios you still have some limits due to AM/FM bandwidth, plus radios differentiate with genres so 30% time on Canada radio means 30% time on rock, rap, jazz, etc.
But TV doesn’t work like that. So I wonder what factors played into the TV quotas not working.
There's a clear quality funnel here: In any creative work, we're really looking for positive outliers. Suppose talent is normally distributed. Increasing the size of the funnel's input means you've got more chances to find the best outliers. If you've got a very tiny funnel, most great actors and cinematographers will become accountants and bicycle racers instead of winning Oscars.