Johnny:
There is more to it. A Sakadagami enjoys pleasures or whatever his heart was set on that was of a sensuous nature, however subtle, for at most 9 billion years ‘only’and pays the price by the suffering he is largely unable to see now. An Anagami is absorbed for 1000 to 16000 mahakalpas in mental bliss IN SOLITUDE, which is deeper than that resulting from contact with anything or anyone outside, so the ‘mental suffering’ that goes with it must be more subtle and therefore more’agonizing’.
So the finer the realm, the more subtle and the more prolonged the experiencing – but that goes for both the enjoyment and the suffering attached to it. As you say, the most ‘efficient’ way would be to attain Nibbana in a human bhava, but that is difficult, to say the least. Also, the ‘going beyond’ of sensuous, if not sensual, pleasures is hard to do. Therefore, as I see at least, the gap or decisive ‘leap’, is not from Sotapanna to Sakadagami, but from Sakadagami to Anagami.