Like Superman using his speed in ways that would quite literally enable him to time travel in one issue, have issues catching up with missiles being spammed across the globe in another, shapeshifting, inconsistent displays of telepathy, etc.
He literally developed powers or used his powers in ways as the plot called for it. Doesn't mean they didn't happen, but they were certainly dictated by whatever the writer felt like at the time.
Which brings me back to my point being that it depends on what kind of day Superman's having and where in the Pre-Crisis era you're taking feats from.
What are you talking about? I don't recall him having trouble with missiles anytime, do you have the scans. Once in DCP 41 he collected thousands of missiles all over the world just under the speed of light because he feared that going faster would make him go into timestream. Shape-shifting was nothing but precise muscle control which was the explanation how Kal-L was not recognized on earth-2. He has demonstrated telepathy on many occasions and if we're on that route why don't we remove the powers displayed by thor and surfer which were never to be seen again. As again no more of a plot-device than mjolnir or power cosmic or hulk's anger etc. Just because "LOLZ ITS DA SLIVER AGEEE" doesn't mean his absurd low showings which mind you aren't bad compared to like of thor and surfer aren't PIS. You mean like today where recently thor was koed by a jet exploding or paul cornell suddenly revealing that superman needs to breath in space despite years of continuity. It was the same guy just like today's thor is classic thor.