They definitely de-powered him in post-Crisis, yes. But that just shows the limited way DC was thinking.
It's a mistake they make constantly with the character. Now, granted, things pre-Crisis were different than they are now and there was a lot of inconsistency from issue to issue, because continuity didn't matter like it does now. But you can look at any number of characters or stories in the modern day and realize that power levels aren't the problem. Aaron's Thor, the current Silver Surfer, tons of various indie titles, Morrison's All-Star, Lobdell and Pak's runs in the New52......all of these writers have managed at least a year's worth of stories featuring a planet-breaking character.
Seriously, all you need to do is smash two random words together and you've got a threat.
Okay, I just used a random word generator and this is what I ended up with.
"Massive" "Visitor"
"Thinkable" "Curve"
"Noise" "Frogs"
I dunno about you, but each pairing gives me several ideas for stuff that could challenge a highly powerful Superman, or at least provide a fun tale. A new Galactus type foe, a sentient geometric shape, hypersonic frog experiments....you could manage at least 18 months of stories just from these three things....and all this took me less than three minutes.