I disagree. FF plans have not changed T&C substantially since AA introduced the first one (in 1984!). As their scope has increased (to become the largest single currency in circulation in the world, per The Economist, surpassing USD in circulation), so have the award point requirements. But there has been little or no change in complexity.
And some of the complexity (e.g. the 10-tier banding in the QFF plan) works to the customers' advantage in aggregate.