The challenges facing spinners in modern limited overs cricket is that there's no room for a loose ball every over. Anything remotely short or pitched up, even worse full toss is dispatched for a 4 if lucky, or most likely a 6.
With the advent of global T20 league cricket, top batsmen in all teams will be brutal against mediocre spin bowling, especially in the last 15 years. Previously batsmen outside Asia were perceived to be weak against spin, not anymore. Introducing spin was plan B for Asian teams with a weak pace attack, like India and Sri Lanka.
The likes of Ajmal, Yasin Shah to certain extent Afridi bowled against batsmen who wanted to see them off, not attack them, they played in an easier era. They used to get away with 1-2 loose balls an over.
Pin point accuracy is important for modern spinners in limited overs cricket. The ability to string together a good over with 6 sharp deliveries is a must to be recognised as a good spinner.
The game has moved on and the bar has been raised. No one ever imagined a time where the likes of New Zealand or Australia would have more competitive spinners.