It must be noted, Aldous, that what Superman learned in the Sandman Saga had more to do with the dangers of his power being misused as opposed to him being specifically unworthy to wield it.
I agree, Captain... There is no question that Superman is the only man worthy of having so much power -- and it is this quality that makes him Superman, more so than the powers themselves.
But...
When he was at full power at the start of the storyline, he was fully in control and had no moral or judgement lapses.
The time he did foul-up at full power was due to brain damage incurred while he was an ordinary mortal that was made permanent with the return of his invulnerability. A non-brain-damaged Superman would not have been a danger and that was abundantly proven in that very storyline.
I guess the lesson was if he were ever not in perfect mental and moral health, the brain-damaged actions might be an indication of what he'd be capable of (e.g. ruining an entire water system to fix a single leaky faucet).
I think there is more to it than this (as I more or less said in my previous post).
In the first part of the Saga, there is a fantastic quote from Superman: "I've never felt so
confident... knowing that there's absolutely
nothing that can harm me!
Morgan Edge was
wrong! Power isn't
corrupting... It's
freeing me -- to do
unlimited good!"
Actually, that is probably my favourite Superman quote ever.
In the last part of the Saga, Superman is saying: "
No! I've seen the
dangers [of] having
too much power... I am human -- I can make mistakes! I don't
want -- or
need -- more..."
The crisis with the brain damage is clearly past, and most unlikely to be repeated. I don't think Superman has this specific crisis in the back of his mind when he is talking to Ching at the end. He has had a complete change of attitude from his earlier "arrogance" (if it can be called that).
It is not so much that Superman is unworthy of having so much power (he is not), but that
he now believes he is unworthy. Big difference.